844 research outputs found
Probing the phonon surface interaction by wave packet simulation: effect of roughness and morphology
One way to reduce the lattice thermal conductivity of solids is to induce
additional phonon surface scattering through nanostructures. However, how
phonons interact with boundaries, especially at the atomic level, is not well
understood. In this work, we performed two-dimensional atomistic wave packet
simulations to investigate the phonon surface interaction. Emphasis has been
given to the angular-resolved phonon reflection at smooth, periodically rough,
and amorphous surfaces. We found that the acoustic phonon reflection at a
smooth surface is not simply specular. Mode conversion can occur after
reflection, and the detailed energy distribution after reflection will
dependent on surface condition and polarization of incident phonon. At
periodically rough surfaces, the reflected wave packet distribution does not
follow the well-known Ziman's model, but shows a nonmonotonic dependence on the
depth of surface roughness. When an amorphous layer is attached to the surface,
the incident wave packet will be absorbed by the amorphous region, and results
in quite diffusive reflection. Our results clearly show that the commonly used
specular-diffusive model is not enough to describe the phonon reflection at a
periodically rough surface, while an amorphous layer can induce strong
diffusive reflection. This work provides a careful analysis of phonon
reflection at a surface with different morphology, which is important to a
better understanding of thermal transport in various nanostructures.Comment: 15pages, 9 figure
On Convergence of Tracking Differentiator with Multiple Stochastic Disturbances
In this paper, the convergence and noise-tolerant performance of a tracking
differentiator in the presence of multiple stochastic disturbances are
investigated for the first time. We consider a quite general case where the
input signal is corrupted by additive colored noise, and the tracking
differentiator itself is disturbed by additive colored noise and white noise.
It is shown that the tracking differentiator tracks the input signal and its
generalized derivatives in mean square and even in almost sure sense when the
stochastic noise affecting the input signal is vanishing. Some numerical
simulations are performed to validate the theoretical results
Signaling transduction regulated by 5-hydroxytryptamine 1A receptor and orexin receptor 2 heterodimers
As G-protein-coupled receptors (GPCRs), 5-hydroxytryptamine 1A receptor (5-HT1AR) and orexin receptor 2 (OX2R) regulate the levels of the cellular downstream molecules. The heterodimers of different GPCRs play important roles in various of neurological diseases. Moreover, 5-HT1AR and OX2R are involved in the pathogenesis of neurological diseases such as depression with deficiency of hippocampus plasticity. However, the direct interaction of the two receptors remains elusive. In the present study, we firstly demonstrated the heterodimer formation of 5-HT1AR and OX2R. Exchange protein directly activated by cAMP (Epac) cAMP bioluminescence resonance energy transfer (BRET) biosensor analysis revealed that the expression levels of cellular cAMP significantly increased in HEK293T cells transfected with the two receptors compared with the 5-HT1AR group. Additionally, the cellular level of calcium was upregulated robustly in HEK293T cells co-transfected with 5-HT1AR and OX2R group after agonist treatment. Furthermore, western blotting data showed that 5-HT1AR and OX2R heterodimer decreased the levels of phosphorylation of extracellular signal-regulated kinase (ERK) and cAMP-response element-binding protein (CREB). These results not only unraveled the formation of 5-HT1AR and OX2R heterodimer but also suggested that the heterodimer affected the downstream signaling pathway, which will provide new insights into the function of the two receptors in the brain
Clay minerals in the Pliocene–Quaternary sediments of the southern Yangtze coast, China: Sediment sources and palaeoclimate implications
AbstractClay mineralogy was used as an indicator of the sediment source and prevailing climate and five suites (I–V) were identified throughout the borehole. Smectite was dominant in the bottom suite of the borehole, indicating the sediment was mainly derived from the local basalt when the study area stood as uplands during the Pliocene. The sharp reduction of smectite in suites II and III (Early Pleistocene) reflects a broader sediment provenance due to neo-tectonic subsidence of the study area. Significant climate fluctuations are indicated by distinct variations in the ratios of illite versus smectite and kaolinite, and by the illite crystallinity in suites II and IV. Especially the suite IV, which forms mottled muddy sediments that underwent pedogenesis, possibly represents glacial/interglacial cycles during the Mid-Pleistocene climate transition (MPT). The rare presence of smectite in suite V which formed during the Late Quaternary suggests a significant contribution of fine-grained sediment derived from the upstream of the Yangtze catchment. Such changes in sediment sources are consistent with the evolution of regional sedimentary environments, which evolved towards an open coast/deltaic setting and imply that the study area became the depositional basin of the Yangtze fine-grained sediment due to the final submergence of the Wu-Nan-Sha and Fukien-Reinan Massifs since the Late Quaternary
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