57 research outputs found
Simulation of emission spectra of transition-metal dichalcogenide monolayers with the multimode Brownian oscillator model
The multimode Brownian oscillator model is employed to simulate the emission
spectra of transition metal dichalcogenide monolayers. Good agreement is
obtained between measured and simulated photoluminescence spectra of WSe2, WS2,
MoSe2 and MoS2 at various temperatures. The Huang-Rhys factor extracted from
the model can be associated with that from the modified semi-empirical Varshni
equation at high temperatures. Individual mechanisms leading to the unique
temperature-dependent emission spectra of those TMDs are validated by the MBO
fitting, while it is in turn confirmed that the MBO analysis is an effective
method for studying the optical properties of TMD monolayers. Parameters
extractd from the MBO fitting can be used to explore exciton-photon-phonon
dynamics of TMDs in a more comprehensive model
MEMS 411: Portable Bridge Crane with Pulleys
The bridge crane demonstrates dynamics behavior that the flexible mode has a natural frequency depending on the string length. In this project, a portable bridge crane is designed and made to demonstrate this dynamical phenomena by changing speed and string length. The portable bridge crane requires a light mass and a small size. At the same time, because it needs to be observed in a two-dimensional plane, the trolley must be able to move horizontally on a bridge with tracks, and the speed of the trolley needs to be controlled by a speed controllable motor. The crane needs to suspend a weight of 1 kg to demonstrate the change in natural frequency. The length of the rope needs to be adjustable. In addition, in order to ensure the stability of the instrument, it is necessary to reduce the impact force of the collision when the trolley hits the ends of the rail. Therefore, a soft stop is necessary to stop the motion of the cart before the collision at the end. In this way, the stability of the structure can be guaranteed in order to avoid tipping due to collision. Our portable bridge crane will demonstrate the effect of changing the speed and the string length on the natural frequency
Exciton Dynamics and Time-Resolved Fluorescence in Nanocavity-Integrated Monolayers of Transition-Metal Dichalcogenides
We have developed an ab-initio-based fully-quantum numerically-accurate
methodology for the simulation of the exciton dynamics and time- and
frequency-resolved fluorescence spectra of the cavity-controlled
two-dimensional materials at finite temperature and applied this methodology to
the single-layer WSe2 system. This allowed us to establish dynamical and
spectroscopic signatures of the polaronic and polaritonic effects as well as
uncover their characteristic timescales in the relevant range of temperatures
Expansion dynamics of a spherical Bose-Einstein condensate
We experimentally and theoretically observe the expansion behaviors of a
spherical Bose-Einstein condensate. A rubidium condensate is produced in an
isotropic optical dipole trap with an asphericity of 0.037. We measure the
variation of the condensate size during the expansion process. The free
expansion of the condensate is isotropic, which is different from that of the
condensate usually produced in the anisotropic trap. The expansion in the short
time is speeding and then after a long time the expansion velocity
asymptotically approaches a constant value. We derive an analytic solution of
the expansion behavior based on the spherical symmetry, allowing a quantitative
comparison with the experimental measurement. The interaction energy of the
condensate is gradually converted into the kinetic energy at the beginning of
the expansion and the kinetic energy dominates after a long-time expansion. We
obtain the interaction energy of the condensate in the trap by probing the
expansion velocity, which is consistent with the theoretical prediction.Comment: 6 pages, 5 figure
An analysis of single and two stage, mesophilic and thermophilic high rate systems for anaerobic digestion of corn stalk
Occurrence and Concentrations of Halogenated Flame Retardants in the Atmospheric Fine Particles in Chinese Cities
In Situ Assembly of Ultrathin PtRh Nanowires to Graphene Nanosheets as Highly Efficient Electrocatalysts for the Oxidation of Ethanol
One-dimensional (1D)
anisotropic platinum-based nanowires are promising electrocatalysts
in polymer electrolyte membrane fuel cells owing to the inherent structural
merits. Herein, we report an in situ growth of ultrathin PtRh nanowires
(diameters of 2â3 nm) on graphene nanosheets via the oriented
attachment pathway. Mechanistic studies reveal that graphene nanosheets
play a critical role in the nucleation and growth of PtRh nanowires.
The resulting hybrid of PtRh nanowire decorated graphene nanosheets
shows outstanding activity and durability toward ethanol electro-oxidation.
It exhibits a specific current density of 2.8 mA cm<sup>â2</sup> and a mass-normalized current density of 1 A mg<sup>â1</sup> metal, which are 5.4 and 3.1 times those of the state-of-the-art
Pt/C catalyst, respectively. After 2000 cyclic tests, it maintains
86% of the initial electrochemically active surface area, which is
larger than that of 63% obtained from the Pt/C catalyst. The superior
performance is attributed to the combination of the advantageous 1D
morphological motif with the synergistic effects of PtRh alloys and
graphene nanosheet support
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