6,017 research outputs found
Breakdown of the interlayer coherence in twisted bilayer graphene
Coherent motion of the electrons in the Bloch states is one of the
fundamental concepts of the charge conduction in solid state physics. In
layered materials, however, such a condition often breaks down for the
interlayer conduction, when the interlayer coupling is significantly reduced by
e.g. large interlayer separation. We report that complete suppression of
coherent conduction is realized even in an atomic length scale of layer
separation in twisted bilayer graphene. The interlayer resistivity of twisted
bilayer graphene is much higher than the c-axis resistivity of Bernal-stacked
graphite, and exhibits strong dependence on temperature as well as on external
electric fields. These results suggest that the graphene layers are
significantly decoupled by rotation and incoherent conduction is a main
transport channel between the layers of twisted bilayer graphene.Comment: 5 pages, 3 figure
Evolution of rubisco complex small subunit transit peptides from algae to plants
Chloroplasts evolved from a free-living cyanobacterium acquired by the ancestor of all photosynthetic eukaryotes, including algae and plants, through a single endosymbiotic event. During endosymbiotic conversion, the majority of genes in the endosymbiont were transferred to the host nucleus and many of the proteins encoded by these genes must therefore be transported into the chloroplast after translation in the cytosol. Chloroplast-targeted proteins contain a targeting signal, named the transit peptide (TP), at the N-terminus. However, the evolution of TPs is not well understood. In this study, TPs from RbcS (rubisco small subunit) were compared between lower and higher eukaryotes. Chlamydomonas reinhardtii RbcS (CrRbcS) TP was non-functional in Arabidopsis. However, inclusion of a critical sequence motif, FP-RK, from Arabidopsis thaliana RbcS (AtRbcS) TP allowed CrRbcS TP to deliver proteins into plant chloroplasts. The position of the FP-RK motif in CrRbcS TP was critical for function. The QMMVW sequence motif in CrRbcS TP was crucial for its transport activity in plants. CrRbcS TPs containing additional plant motifs remained functional in C. reinhardtii. These results suggest that TPs evolved by acquiring additional sequence motifs to support protein targeting to chloroplasts during evolution of land plants from algae.113Ysciescopu
SPANet: Frequency-balancing Token Mixer using Spectral Pooling Aggregation Modulation
Recent studies show that self-attentions behave like low-pass filters (as
opposed to convolutions) and enhancing their high-pass filtering capability
improves model performance. Contrary to this idea, we investigate existing
convolution-based models with spectral analysis and observe that improving the
low-pass filtering in convolution operations also leads to performance
improvement. To account for this observation, we hypothesize that utilizing
optimal token mixers that capture balanced representations of both high- and
low-frequency components can enhance the performance of models. We verify this
by decomposing visual features into the frequency domain and combining them in
a balanced manner. To handle this, we replace the balancing problem with a mask
filtering problem in the frequency domain. Then, we introduce a novel
token-mixer named SPAM and leverage it to derive a MetaFormer model termed as
SPANet. Experimental results show that the proposed method provides a way to
achieve this balance, and the balanced representations of both high- and
low-frequency components can improve the performance of models on multiple
computer vision tasks. Our code is available at
.Comment: Accepted paper at ICCV 202
Nonequilibrium fluctuations for a single-particle analog of gas in a soft wall
We investigate the motion of a colloidal particle driven out of equilibrium by a time-varying stiffness of the optical trap that produces persistent nonequilibrium work. Measurements of work production for repeated cycles composed of the compression and expansion processes for the optical potential show huge fluctuations due to thermal motion. Using a precise technique to modulate the stiffness in time, we accurately estimate the probability distributions of work produced for the compression and expansion processes. We confirm the fluctuation theorem from the ratio of the two distributions. We also show that the average values of work for the two processes comply with the Jarzynski equality. This system has an analogy with a gas in a breathing soft wall. We discuss about its applicability to a heat engine and an information engine operated by feedback control.open1
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