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  • 1
    Electronic Resource
    Electronic Resource
    Elastic buckling of honeycomb structure under out-of-plane pressure (1991)
    Springer
    Acta mechanica solida Sinica 4 (1991), S. 449-455 
    Details
    ISSN: 0894-9166
    Keywords: out-of-plane ; honeycomb structure ; elastic buckling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract A theoretical model and an analytical method, which are suitable for initial elastic buckling analysis of two-dimensional honeycomb structures including hexagonal honeycombs with walls of equal or unequal thickness, rectangular and triangular honeycombs etc., are developed in this paper. The results given in present paper agree well with the experimental data of hexagonal honeycombs with walls of unequal thickness.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02207593
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  • 2
    Electronic Resource
    Electronic Resource
    Optical transient bleaching of quantum-confined CdS clusters: The effects of surface-trapped electron–hole pairs (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 6927-6939 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We studied the optical transient bleaching of ∼40 A(ring), ammonia-passivated CdS clusters in a polymer with nanosecond and picosecond pump-probe techniques. The transient bleaching spectra behave differently in different time regimes. Within the 30-ps pump laser pulse width, we tentatively attribute the bleaching to the exciton-exciton interaction, and the magnitude can be enhanced by surface passivation. On time scales of tens of picoseconds and longer following the pump pulse, when only trapped electron-hole pairs remain from the pump excitation, the bleaching is due to the interaction between such a trapped electron-hole pair and a bound exciton produced by the probe light. Experimentally we determined that roughly one trapped electron-hole pair can bleach the excitonic absorption of the whole CdS cluster. We developed a theoretical model which considers the effects of the trapped electron-hole pair on the energy of the exciton transition and its oscillator strength. We found that, when a trapped electron and hole are present, the lowest exciton absorption is red-shifted from the original exciton absorption, and this transition has a weak oscillator strength, which explains the observed efficient bleaching. The model also predicts that a trapped electron is more efficient than a trapped hole for bleaching the excitonic absorption of CdS clusters in the size regime considered here. This is confirmed by pulse radiolysis results. Finally, we discuss the possible effects of charged surface defects on the linear absorption spectra of semiconductor clusters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458280
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  • 3
    Electronic Resource
    Electronic Resource
    A picosecond bleaching study of quantum-confined cadmium sulfide microcrystallites in a polymer film (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 3435-3441 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report a picosecond pump–probe study of 55 A(ring) cadmium sulfide microcrystallites embedded in polymer films. Large negative absorbance changes at wavelengths corresponding to energies near the band gap are observed. This absorption bleaching and the associated changes in refractive index are mainly responsible for the large nonlinearity observed in degenerate four-wave mixing experiments. Based on photoluminescence data, the known electron-trapping cross section of defects, and these pump–probe experiments, we show that the conventional carrier density-dependent band-filling mechanism cannot account for the data, and the absorption bleaching is due to the saturation of the excitonic transition. We further show that the phase-space filling and exchange effects from exciton–exciton and exciton-free carrier interactions fail to account for the observed data. Instead, we propose that the exciton-trapped carrier interaction is mainly responsible for the observed bleaching of the excitonic absorption. This interaction is unique for small semiconductor clusters since the presence of a high density of defects (most likely on the surfaces) causes the extremely rapid trapping of free carriers. According to this model, the recovery time of the absorption bleaching is determined by the trapped-carrier relaxation time, which is sensitive to the fabrication methods and can be controlled by surface chemistry. Our study also demonstrates that one needs to understand the effects of surfaces and control the surface chemistry before the important question of size effects on the nonlinear optical properties can be addressed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454913
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  • 4
    Electronic Resource
    Electronic Resource
    Nonresonant third-order optical nonlinearity of quantum-confined CdS clusters: A third harmonic generation study (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 3417-3419 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the first study, to the best of our knowledge, of the nonresonant third-order optical nonlinearity of quantum-confined CdS clusters using third harmonic generation from 1.91 to 0.64 μm. We observe that the nonlinearity increases with the increase in the cluster size. The intrinsic, nonresonant χ(3)CdS for ∼30, ∼15 A(ring) thiophenolate-capped CdS clusters and [Cd10S4(SPh)16]−4 molecular clusters are 3.3×10−10, 2.5×10−11, 4.7×10−12 esu, respectively. To utilize this large nonresonant nonlinearity it is necessary to incorporate these clusters into a sample in high concentrations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.344096
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  • 5
    Electronic Resource
    Electronic Resource
    Dielectric function of solid C70 films (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 61 (1992), S. 124-126 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using variable-angle ellipsometry and normal incidence reflection/transmission optical techniques we have measured the dielectric function ε(ω) at room temperature for solid C70 films over the photon energy range 0.5≤E≤5.3 eV. The onset of absorption across the highest-occupied-molecular-orbit (HOMO)–lowest-unoccupied-molecular-orbit (LUMO) gap is measured to be 1.25 eV. Furthermore, structure in the interband absorption at 2.41, 3.10, 3.50, and 4.45 eV is observed. The refractive index at zero frequency is estimated to be n(0)=1.94 as compared to the value n(0)=1.90, which we obtained for solid C60 from our previous study.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.108248
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  • 6
    Electronic Resource
    Electronic Resource
    Optical fiber sensor for berberine based on fluorescence quenching of 2-(4-diphenylyl)-6-phenylbenzoxazole (1998)
    Springer
    Fresenius' journal of analytical chemistry 360 (1998), S. 702-706 
    Details
    ISSN: 1432-1130
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A new optical fiber sensor was prepared for the determination of berberine in aqueous solution using a micrometer-sized flow-cell and a bifurcated optical fiber. The sensing is based on fluorescence quenching of 2-(4-diphenylyl)-6-phenylbenzoxazole (PBBO) in the PVC membrane. This process is accompanied by non-fluorescent ground-state complex formation. With this sensor, berberine can be determined in sample solutions from 2.42 × 10–5 mol L–1 to 6.04 × 10–7 mol L–1. Satisfactory reproducibility, reversibility, and short response times of less than 1 min are realized. The sensor also shows good selectivity over some common pharmaceutical species and alkali and alkali-earth metal salts, and can be used for the direct assay of berberine in commercial tablets. The results are in correspondence with those obtained by the pharmacopoeia method.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002160050785
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  • 7
    Electronic Resource
    Electronic Resource
    Optosensing of hydrochloric acid based on the fluorescence quenching of a flavone copolymer (1998)
    Springer
    Fresenius' journal of analytical chemistry 362 (1998), S. 387-390 
    Details
    ISSN: 1432-1130
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract An optical fiber sensor for the continuous determination of hydrochloric acid is presented. It is based on the fluorescence quenching of a flavone containing copolymer membrane by hydrochloric acid. The quenching efficiency is greatly enhanced in the presence of Fe(III). This enhancement is attributed to the primary inner filter effect, as well as the formation of a complex between the 4′-N,N-dimethylaminoflavone group in the copolymer and the Fe(III) species extracted from hydrochloric acid solution. The optical response is linear and reversible for 0.10–6.00 mol L–1 HCl with a response time of the order of a second. The standard deviations for repeated alternative measurements of 0.20 and 2.00 mol L–1 hydrochloric acid are 0.32% and 0.46% (n = 10), respectively, indicating a good reproducibility. Because of the covalently bonding of the dye to polymer, the sensor exhibits also a good stability. Selectivity has also been evaluated for some potential interferents. The sensor in conjunction with a flow-injection system can be used for on-line determination of hydrochloric acid.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002160051090
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  • 8
    Electronic Resource
    Electronic Resource
    Expression of Bcl-2 protein in the epiphyseal plate cartilage and trabecular bone of growing rats (1997)
    Springer
    Histochemistry and cell biology 108 (1997), S. 45-55 
    Details
    ISSN: 1432-119X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract  The protooncogene protein, Bcl-2, protects cells from apoptosis and ensures their survival in vitro by inhibiting the action of the apoptosis-inducer, Bax. Its expression in proliferative and long-lived cells in vivo also indicates that it protects against cell death. The chondrocytes of the epiphyseal plate cartilage undergo a series of maturation steps and deposit mineral in the cartilage matrix before dying. The possibility that Bcl-2 helps protect chondrocytes until mineral deposition is completed was investigated by determining the distribution of Bcl-2 immunoreactivity in the epiphyseal plate cartilage of growing rats and its subcellular localization, using a specific antibody. The involvement of Bax in the triggering of chondrocyte death was checked by immunocytochemistry. Bcl-2 expression in the osteoblasts and the final result of their evolution, the osteocytes, was also examined in trabecular bone. Bcl-2 immunoreactivity was non-uniformly distributed throughout the epiphyseal cartilage. It was maximal in proliferative chondrocytes, decreased in mature chondrocytes, and low in hypertrophic chondrocytes, whereas there was Bax immunoreactivity in all chondrocytes examined. Immunolabeling was intense in osteoblasts but considerably lower in fully differentiated osteocytes. Bcl-2 immunoreactivity was mainly in the cytoplasm of chondrocytes, osteoblasts, and early osteocytes; the nuclei appeared clear. The subcellular distribution of Bcl-2 immunolabeling in chondrocytes, revealed by gold particles in the electron microscope, showed that gold particles were frequently concentrated in the mitochondria in all the cartilage zones and lay mainly within the organelles, not at their periphery. The endoplasmic reticulum contained moderate immunoreactivity and there were few gold particles in the cytoplasm and nuclei. The number of gold particles decreased in all the subcellular compartments from proliferative to hypertrophic chondrocytes. In contrast, Bax immunoreactivity changed little during chondrocyte terminal evolution, and its subcellular distribution mirrored that of Bcl-2. These immunocytochemical data indicate that Bcl-2 helps maintain chondrocytes and osteoblasts until their terminal maturation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004180050145
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  • 9
    Electronic Resource
    Electronic Resource
    Input synchrony and spike-timing dependent plasticity (2003)
    Springer
    The European physical journal 31 (2003), S. 385-390 
    Details
    ISSN: 1434-6036
    Keywords: PACS. 87.18.Sn Neural networks – 87.16.Xa Signal transduction – 87.17.Aa Theory and modeling; computer simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: The influence of a weight-dependent spike-timing dependent plasticity (STDP) rule on the temporal evolution and equilibrium state of a certain synapse is investigated. We show that under certain conditions, a spike-induced rate-learning scheme could be achieved. Through studying the situation when a single Hodgkin-Huxley neuron is driven by a large ensemble of input neurons, we find that synchronized firing of a sub population of input neurons may be important to information processing in the nervous system. Using simulations, we show that the temporal structure of the spike trains of these synchronized input neurons can be transmitted reliably; further, synapses from these neurons will increase stably due to the STDP rule and this may provide a mechanism for learning and information storage in biologically plausible network models.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1140/epjb/e2003-00046-2
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  • 10
    Electronic Resource
    Electronic Resource
    Biosynthesis and Characterization of 4-Fluorotryptophan-Labeled Escherichia coli Arginyl-tRNA Synthetase (1999)
    Springer
    The protein journal 18 (1999), S. 187-192 
    Details
    ISSN: 1573-4943
    Keywords: Arginyl-tRNA synthetase ; 4-fluorotryptophan ; 19F NMR ; HPLC
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Escherichia coli 4-fluorotryptophan-substituted arginyl-tRNA synthetase was biosynthetically prepared and purified from a tryptophan auxotroph which could overproduce this enzyme. A method was developed to separate 4-fluorotryptophan from tryptophan and to determine accurately their contents in the 4-fluorotryptophan-containing proteins. It was confirmed that more than 95% of the tryptophan residues in the purified 4-fluorotryptophan-substituted arginyl-tRNA synthetase were replaced by 4-fluorotryptophan. Studies on the effect of the 4-fluorotryptophan replacement on properties of the enzyme showed that, when compared with the native enzyme, both the specific activity and the first-order rate constant of the fluorinated enzyme decreased by approximately 20% with just slightly higher K m values. CD studies, however, did not reveal any difference between the secondary structure of the native and fluorinated enzymes. In addition, thermal unfolding studies showed that the 4-fluorotryptophan replacement did not significantly affect the thermal stability of the enzyme. We may conclude that the substitution of 4-fluorotryptophan in arginyl-tRNA synthetase had no substantial effect on the structure and function of the enzyme. Finally, a preliminary study of 19F nuclear magnetic resonance spectroscopy of the fluorinated enzyme has shown promising prospect for further investigation of its structure and function with NMR.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1020675922382
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