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排序方式: 共有212条查询结果,搜索用时 15 毫秒
11.
12.
The fluorescence mode confocal laser scanning microscopy (CLSM) is introduced as an alternative method to investigate the
bulk structure of poly(vinyl alcohol) (PVA) hydrogel. Investigations of the bulk structure of hydrogel samples, prepared by
freezing and controlled thawing of aqueous PVA solutions followed by fluorochrome conjugation, were possible in the native
state because with this technique water does not need to be removed prior to examination. This is of advantage to other methods,
such as scanning electron microscopy, requiring dehydration by critical-point drying or freeze-etching, because both may result
in a significant alteration of the gel structure. CLSM images of the hydrogel bulk structure were taken at several successive
intervals from the surface into the hydrogel (up to 60 μm) without freeze-fracturing or cutting the sample. Detailed morphological
characterization is achievable by superimposing series of images taken at successive intervals and by magnifying special regions
of interest. Images of hydrogel bulk structures revealed a continuous, three-dimensional network that originates from phase-separation
(spinodal decomposition) during the freezing period. The pore or mesh size in the cryogel increased, from about 2–7 μm, with
decreasing PVA concentration. The surface layer was only a few microns thick, and the bulk structure underneath showed neither
porosity gradients nor structural orientations.
Received: 29 April 2000/Accepted: 18 August 2000 相似文献
13.
Keil R Perez-Leija A Dreisow F Heinrich M Moya-Cessa H Nolte S Christodoulides DN Szameit A 《Physical review letters》2011,107(10):103601
Coherent states and their generalizations, displaced Fock states, are of fundamental importance to quantum optics. Here we present a direct observation of a classical analogue for the emergence of these states from the eigenstates of the harmonic oscillator. To this end, the light propagation in a Glauber-Fock waveguide lattice serves as equivalent for the displacement of Fock states in phase space. Theoretical calculations and analogue classical experiments show that the square-root distribution of the coupling parameter in such lattices supports a new family of intriguing quantum correlations not encountered in uniform arrays. Because of the broken shift invariance of the lattice, these correlations strongly depend on the transverse position. Consequently, quantum random walks with this extra degree of freedom may be realized in Glauber-Fock lattices. 相似文献
14.
We show that the geometrically induced potential existing in undulated slab waveguides dramatically affects the properties of solitons. In particular, whereas solitons residing in the potential maxima do not feature power thresholds and are stable, their counterparts residing in the potential minima are unstable and may exhibit a power threshold for their existence. Additionally, the geometric potential is shown to support stable multipole solitons that cannot be supported by straight waveguides. Finally, the geometric potential results in the appearance of the effective barriers that prevent transverse soliton motion. 相似文献
15.
Short-pulse optical sources have allowed the study of ultrafast electrical phenomena in the circuits and devices which will become future electronic systems. In this paper techniques for the generation, propagation and detection of electrical signals in the femtosecond regime are presented. 相似文献
16.
Arnaldi R Banicz K Castor J Chaurand B Cicalò C Colla A Cortese P Damjanovic S David A de Falco A Devaux A Ducroux L En'yo H Fargeix J Ferretti A Floris M Förster A Force P Guettet N Guichard A Gulkanian H Heuser JM Keil M Kluberg L Lourenço C Lozano J Manso F Martins P Masoni A Neves A Ohnishi H Oppedisano C Parracho P Pillot P Poghosyan T Puddu G Radermacher E Ramalhete P Rosinsky P Scomparin E Seixas J Serci S Shahoyan R Sonderegger P Specht HJ Tieulent R Usai G Veenhof R 《Physical review letters》2007,99(13):132302
The NA60 experiment studies muon pair production at the CERN Super Proton Synchrotron. In this Letter we report on a precision measurement of J/psi in In-In collisions. We have studied the J/psi centrality distribution, and we have compared it with the one expected if absorption in cold nuclear matter were the only active suppression mechanism. For collisions involving more than approximately 80 participant nucleons, we find that an extra suppression is present. This result is in qualitative agreement with previous Pb-Pb measurements by the NA50 experiment, but no theoretical explanation is presently able to coherently describe both results. 相似文献
17.
Miller SA Hiatt LA Keil RG Wright DW Cliffel DE 《Analytical and bioanalytical chemistry》2011,399(3):1021-1029
Immunoassays are important tools for the rapid detection and identification of pathogens, both clinically and in the research
laboratory. An immunoassay with the potential for the detection of influenza was developed and tested using hemagglutinin
(HA), a commonly studied glycoprotein found on the surface of influenza virions. Gold nanoparticles were synthesized, which
present multiple peptide epitopes, including the HA epitope, in order to increase the gravimetric response achieved with the
use of a QCM immunosensor for influenza. Specifically, epitopes associated with HA and FLAG peptides were affixed to gold
nanoparticles by a six-mer PEG spacer between the epitope and the terminal cysteine. The PEG spacer was shown to enhance the
probability for interaction with antibodies by increasing the distance the epitope extends from the gold surface. These nanoparticles
were characterized using thermogravimetric analysis, transmission electron microscopy, matrix-assisted laser desorption/ionization-time
of flight, and 1H nuclear magnetic resonance analysis. Anti-FLAG and anti-HA antibodies were adhered to the surface of a QCM, and the response
of each antibody upon exposure to HA, FLAG, and dual functionalized nanoparticles was compared with binding of Au–tiopronin
nanoparticles and H5 HA proteins from influenza virus (H5N1). Results demonstrate that the immunoassay was capable of differentiating
between nanoparticles presenting orthogonal epitopes in real-time with minimal nonspecific binding. The detection of H5 HA
protein demonstrates the logical extension of using these nanoparticle mimics as a safe positive control in the detection
of influenza, making this a vital step in improving influenza detection methodology. 相似文献
18.
Theoretical rate constants have been calculated for O(3P) with five saturated hydrocarbons, CH4, C2H6, C3H8, iso-C4H10, and neo-C5H12. The method of choice is bond energy–bond order (BEBO) with activated complex theory (ACT). Because the BEBO method is empirical, O(3P) + CH4 is evaluated first, and the theoretical results are compared to more rigorous calculations and to the empirical transition state method. Comparisons are also made between predictions and experimental results. All of these comparisons show that the BEBO-ACT method gives results which are consistent with experiment and other theory. Because the method is successful, the other four cases are then considered. Ambiguity arises for the higher hydrocarbons from the problem of internal rotations in the activated complexes, and three cases are evaluated. Best agreement with experiment is obtained if the primary rotor(s) in the complexes are considered to be free. Predictions of rate constants are made from 500 to 2500 K. Throughout the discussion issues of theory which are common to any ACT calculation from any method of potential energy evaluation (LEP, LEPS, or ab initio quantum mechanics) are featured. 相似文献
19.
New experimental data have been obtained for H + C2H2, D + C2H2, H + C2D2, and D + C2D2 at room temperature. Two previously described apparatus were used in order to measure the pressure dependence of the reactions. The absolute rate constants are compared to results from other laboratories. The present results and those of Payne and Stief are used to obtain the high-pressure limiting rate constant at room temperature. When the activation energy from the work of Payne and Stief is considered, it is shown that the A factor for H + C2H2 is too low by a factor of ~20. If a transmission coefficient is introduced which is constant for all isotopic variations, the pressure dependence can be explained in terms of the randomly energized radicals. RRKM theory is then invoked to explain the observed statistical nonequilibrium kinetic isotope effects. 相似文献
20.