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981.
Andersen O.K. Fischer A.P.A. Lane I.C. Louvergneaux E. Stolte S. Lenstra D. 《Quantum Electronics, IEEE Journal of》1999,35(4):577-582
We report on a systematic experimental investigation of the dynamical behavior of a diode laser subject to delayed feedback from a phase-conjugating mirror based on nearly-degenerate four-wave mixing in rubidium vapor. We present the first experimental stability diagram for this system. In the weak feedback regime, with feedback levels up to -30 dB, me demonstrate locking to the pump frequency with a reduced linewidth smaller than 8 MHz. In contrast to a laser with external injection, and contrary to predictions made for phase-conjugate feedback, the extent of this locking region is found to be limited. For increased feedback rates, the laser leaves the locking region and enters an unstable region through a series of multiple sidebands spectra. This is associated with self-excitation of the relaxation oscillation, and the observed scenario suggests a series of period-doublings after an initial Hopf bifurcation 相似文献
982.
The capacity of flat fading channels when applying differential encoding with noncoherent reception and no channel state information available at the receiver is considered. Numerical results indicate the gains achievable by multiple symbol detection in the case of slowly time-varying channels and provide a comparison between schemes with different potential bandwidth efficiencies 相似文献
983.
Porosity and catalyst utilization of thin layer cathodes in air operated PEM-fuel cells 总被引:6,自引:0,他引:6
Better performance of and higher electrocatalyst utilization in proton-exchange membrane fuel cells equipped with thin film electrodes is achieved by exploiting pore forming additives in the electrode recipe formulation. Preparing the membrane–electrode assembly by a hot spraying procedure already provides 35% porosity. Additional coarse porosity is obtained by adding pore formers to the electrocatalyst slurry which is used for the hot spraying process. This allows for a better access of oxygen from air to the depth of the cathode. For air operation at ambient pressure and low catalyst loading of 0.15mgPtcm-2 a current density of 200mAcm-2 at 0.7V cell voltage can be obtained with such electrodes. 相似文献
984.
S. V. Ivanov A. A. Toropov S. V. Sorokin T. V. Shubina I. V. Sedova P. S. Kop’ev Zh. I. Alferov A. Waag H. J. Lugauer G. Reuscher M. Keim F. F. Fischer G. Landwehr 《Semiconductors》1999,33(9):1016-1020
We report the results of an experimental study of molecular-beam epitaxy of ZnSe-based laser heterostructures with a new structure
of the active region, which contains a fractional-monolayer CdSe recombination region in an expanded ZnSe quantum well and
a waveguide based on a variably-strained, short-period superlattice are reported. Growth of a fractional-monolayer CdSe region
with a nominal thickness of 2–3 ML, i.e., less than the critical thickness, on a ZnSe surface (Δa/a∼7%) leads to the formation of self-organized, pseudomorphic, CdSe-enriched islands with lateral dimensions ∼10–30 nm and
density ∼2×1010 cm−2, which serve as efficient centers of carrier localization, giving rise to effective spatial separation of defective regions
and regions of radiative recombination and, as a result, a higher quantum efficiency. Laser structures for optical pumping
in the (Zn, Mg) (S, Se) system with a record-low threshold power density (less than 4 kW/cm2 at 300 K) and continuous-wave laser diodes in the system (Be, Mg, Zn) Se with a 2.5 to 2.8-ML-thick, fractional-monolayer
CdSe active region have been obtained. The laser structures and diodes have an improved degradation resistance.
Fiz. Tekh. Poluprovodn. 33, 1115–1119 (September 1999) 相似文献
985.
I. S. Fischer 《Engineering with Computers》1999,15(4):334-344
Derivative operators are developed so that the Fisher–Paul dual-number version of the Uicker–Denavit– Hartenberg iteration
scheme for computing displacements in spatial mechanisms can be applied to the Tracta coupling. The constant-velocity input-output
characteristic of the Tracta coupling is shown and the intermediate-joint displacements are investigated. 相似文献
986.
987.
988.
E. Soppa S. Schmauder G. Fischer J. Thesing R. Ritter 《Computational Materials Science》1999,16(1-4):323-332
In this contribution, investigations of the influence of the microstructure on the macro-, meso- and micro-effects in metal–matrix composites are presented by direct combination of experiment and simulation. The aim of the presented work consists in an improved understanding of the mechanical behaviour of heterogeneous materials by combining information of different length scales. 相似文献
989.
990.
Tobias Fischer Luuk J. G. W. van Wilderen Petra Gnau Jens Bredenbeck Lars-Oliver Essen Josef Wachtveitl Chavdar Slavov 《International journal of molecular sciences》2021,22(19)
The family of phytochrome photoreceptors contains proteins with different domain architectures and spectral properties. Knotless phytochromes are one of the three main subgroups classified by their distinct lack of the PAS domain in their photosensory core module, which is in contrast to the canonical PAS-GAF-PHY array. Despite intensive research on the ultrafast photodynamics of phytochromes, little is known about the primary kinetics in knotless phytochromes. Here, we present the ultrafast Pr ⇆ Pfr photodynamics of SynCph2, the best-known knotless phytochrome. Our results show that the excited state lifetime of Pr* (~200 ps) is similar to bacteriophytochromes, but much longer than in most canonical phytochromes. We assign the slow Pr* kinetics to relaxation processes of the chromophore-binding pocket that controls the bilin chromophore’s isomerization step. The Pfr photoconversion dynamics starts with a faster excited state relaxation than in canonical phytochromes, but, despite the differences in the respective domain architectures, proceeds via similar ground state intermediate steps up to Meta-F. Based on our observations, we propose that the kinetic features and overall dynamics of the ultrafast photoreaction are determined to a great extent by the geometrical context (i.e., available space and flexibility) within the binding pocket, while the general reaction steps following the photoexcitation are most likely conserved among the red/far-red phytochromes. 相似文献