450 research outputs found
swTVM: Exploring the Automated Compilation for Deep Learning on Sunway Architecture
The flourish of deep learning frameworks and hardware platforms has been
demanding an efficient compiler that can shield the diversity in both software
and hardware in order to provide application portability. Among the exiting
deep learning compilers, TVM is well known for its efficiency in code
generation and optimization across diverse hardware devices. In the meanwhile,
the Sunway many-core processor renders itself as a competitive candidate for
its attractive computational power in both scientific and deep learning
applications. This paper combines the trends in these two directions.
Specifically, we propose swTVM that extends the original TVM to support
ahead-of-time compilation for architecture requiring cross-compilation such as
Sunway. In addition, we leverage the architecture features during the
compilation such as core group for massive parallelism, DMA for high bandwidth
memory transfer and local device memory for data locality, in order to generate
efficient code for deep learning application on Sunway. The experimental
results show the ability of swTVM to automatically generate code for various
deep neural network models on Sunway. The performance of automatically
generated code for AlexNet and VGG-19 by swTVM achieves 6.71x and 2.45x speedup
on average than hand-optimized OpenACC implementations on convolution and fully
connected layers respectively. This work is the first attempt from the compiler
perspective to bridge the gap of deep learning and high performance
architecture particularly with productivity and efficiency in mind. We would
like to open source the implementation so that more people can embrace the
power of deep learning compiler and Sunway many-core processor
Crosslinking-induced endocytosis of acetylcholine receptors by quantum dots
In a majority of patients with myasthenia gravis (MG), anti-acetylcholine receptor (AChR) antibodies target postsynaptic AChR clusters and thus compromise the membrane integrity of neuromuscular junctions (NMJs) and lead to muscle weakness. Antibody-induced endocytosis of AChRs in the postsynaptic membrane represents the initial step in the pathogenesis of MG; however, the molecular mechanisms underlying AChR endocytosis remain largely unknown. Here, we developed an approach to mimic the pathogenic antibodies for inducing the crosslinking and internalization of AChRs from the postsynaptic membrane. Using biotin-α-bungarotoxin and quantum dot (QD)-streptavidin, cell-surface and internalized AChRs could be readily distinguished by comparing the size, fluorescence intensity, trajectory, and subcellular localization of the QD signals. QD-induced AChR endocytosis was mediated by clathrin-dependent and caveolin-independent mechanisms, and the trafficking of internalized AChRs in the early endosomes required the integrity of microtubule structures. Furthermore, activation of the agrin/MuSK (muscle-specific kinase) signaling pathway strongly suppressed QD-induced internalization of AChRs. Lastly, QD-induced AChR crosslinking potentiated the dispersal of aneural AChR clusters upon synaptic induction. Taken together, our results identify a novel approach to study the mechanisms of AChR trafficking upon receptor crosslinking and endocytosis, and demonstrate that agrin-MuSK signaling pathways protect against crosslinking-induced endocytosis of AChRs. © 2014 Lee et al.published_or_final_versio
Nonlinear Transport of Graphene in the Quantum Hall Regime
We have studied the breakdown of the integer quantum Hall (QH) effect with
fully broken symmetry, in an ultra-high mobility graphene device sandwiched
between two single crystal hexagonal boron nitride substrates. The evolution
and stabilities of the QH states are studied quantitatively through the
nonlinear transport with dc Hall voltage bias. The mechanism of the QH
breakdown in graphene and the movement of the Fermi energy with the electrical
Hall field are discussed. This is the first study in which the stabilities of
fully symmetry broken QH states are probed all together. Our results raise the
possibility that the v=6 states might be a better target for the quantum
resistance standard.Comment: 15 pages,6 figure
Large area growth and electrical properties of p-type WSe2 atomic layers.
Transition metal dichacogenides represent a unique class of two-dimensional layered materials that can be exfoliated into single or few atomic layers. Tungsten diselenide (WSe(2)) is one typical example with p-type semiconductor characteristics. Bulk WSe(2) has an indirect band gap (∼ 1.2 eV), which transits into a direct band gap (∼ 1.65 eV) in monolayers. Monolayer WSe(2), therefore, is of considerable interest as a new electronic material for functional electronics and optoelectronics. However, the controllable synthesis of large-area WSe(2) atomic layers remains a challenge. The studies on WSe(2) are largely limited by relatively small lateral size of exfoliated flakes and poor yield, which has significantly restricted the large-scale applications of the WSe(2) atomic layers. Here, we report a systematic study of chemical vapor deposition approach for large area growth of atomically thin WSe(2) film with the lateral dimensions up to ∼ 1 cm(2). Microphotoluminescence mapping indicates distinct layer dependent efficiency. The monolayer area exhibits much stronger light emission than bilayer or multilayers, consistent with the expected transition to direct band gap in the monolayer limit. The transmission electron microscopy studies demonstrate excellent crystalline quality of the atomically thin WSe(2). Electrical transport studies further show that the p-type WSe(2) field-effect transistors exhibit excellent electronic characteristics with effective hole carrier mobility up to 100 cm(2) V(-1) s(-1) for monolayer and up to 350 cm(2) V(-1) s(-1) for few-layer materials at room temperature, comparable or well above that of previously reported mobility values for the synthetic WSe(2) and comparable to the best exfoliated materials
Seasonality of global and Arctic black carbon processes in the Arctic Monitoring and Assessment Programme models
This study quantifies black carbon (BC) processes in three global climate models and one chemistry transport model, with focus on the seasonality of BC transport, emissions, wet and dry deposition in the Arctic. In the models, transport of BC to the Arctic from lower latitudes is the major BC source for this region. Arctic emissions are very small. All models simulated a similar annual cycle of BC transport from lower latitudes to the Arctic, with maximum transport occurring in July. Substantial differences were found in simulated BC burdens and vertical distributions, with Canadian Atmospheric Global Climate Model (CanAM) (Norwegian Earth System Model, NorESM) producing the strongest (weakest) seasonal cycle. CanAM also has the shortest annual mean residence time for BC in the Arctic followed by Swedish Meteorological and Hydrological Institute Multiscale Atmospheric Transport and Chemistry model, Community Earth System Model, and NorESM. Overall, considerable differences in wet deposition efficiencies in the models exist and are a leading cause of differences in simulated BC burdens. Results from model sensitivity experiments indicate that convective scavenging outside the Arctic reduces the mean altitude of BC residing in the Arctic, making it more susceptible to scavenging by stratiform (layer) clouds in the Arctic. Consequently, scavenging of BC in convective clouds outside the Arctic acts to substantially increase the overall efficiency of BC wet deposition in the Arctic, which leads to low BC burdens and a more pronounced seasonal cycle compared to simulations without convective BC scavenging. In contrast, the simulated seasonality of BC concentrations in the upper troposphere is only weakly influenced by wet deposition in stratiform clouds, whereas lower tropospheric concentrations are highly sensitive.Key PointsSeasonal variations of black carbon (BC) mass budgets in the Arctic are simulatedGood agreement in simulated annual mean transport of BC to the Arctic in modelsConvective wet removal is important for differences in modeled BC concentrationPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/133539/1/jgrd53064-sup-0001-SI.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/133539/2/jgrd53064.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/133539/3/jgrd53064_am.pd
Interannual variation of summer sea surface temperature in the Amundsen Sea, Antarctica
This paper investigates the interannual variability of January sea surface temperature (SST) in the Amundsen Sea (AS) during the period 1982–2022. SST in the Pine Island Bay (PIB) is found to exhibit the most significant interannual variation, with a standard deviation up to 0.6°. Composite analysis indicates that, in warmer years, the January SST at PIB is approximately 1° higher on average than that in cooler years, and its variation in warmer (cooler) years corresponds to lower (higher) sea ice concentration (SIC) and more (less) surface heat flux; the latter factor is primarily influenced by the albedo of SIC. Further analysis suggests that variability in January SIC is largely dominated by northward sea ice motion during the previous November (r = −0.82), which is consistent with the presence of a contemporaneous northerly 10 m wind anomaly trigged by the Amundsen Sea Low (ASL). The ASL-associated northerly wind anomaly drives northward sea ice motion, reduces SIC, and thus increases the downward heat flux that ultimately results in warmer SST, and vice versa. This study identifies the possible mechanism of anomalous January SST in the PIB, which could provide an important clue for seasonal forecasts of summer SST in the AS
Valley Isospin Controlled Fractional Quantum Hall States in Bilayer Graphene
A two-dimensional electron system placed in a magnetic field develops Landau
levels, where strong Coulomb interactions lead to the appearance of many-body
correlated ground states. Quantum numbers similar to the electron spin enable
the understanding and control of complex ground state order and collective
excitations. Owing to its spin, valley and orbital degrees of freedom,
Bernal-stacked bilayer graphene offers a rich platform to pursue correlated
phenomena in two dimensions. In this work, we fabricate dual-gated
Bernal-stacked bilayer graphene devices and demonstrate unprecedented fine
control over its valley isospin degrees of freedom using a perpendicular
electric field. Higher sample quality enables us to probe regimes obscured by
disorder in previous studies. We present evidence for a new even-denominator
fractional quantum Hall state at filling factor {\nu} = 5/2. The 5/2 state is
found to be spontaneously valley polarized in the limit of vanishing valley
Zeeman splitting, consistent with a theoretical prediction made regarding the
spin polarization of the Moore-Read state. In the vicinity of the
even-denominator fractional quantum Hall states, we observe the appearance of
the predicted Levin-Halperin daughter states of the Moore-Read Pfaffian wave
function at {\nu}= 3/2, 7/2 and of the anti-Pfaffian at {\nu}= 5/2 and -1/2.
These observations suggest the breaking of particle-hole symmetry in bilayer
graphene. We construct a comprehensive valley polarization phase diagram for
the Jain sequence fractional states surrounding filling factor 3/2. These
results are well explained by a two-component composite fermion model, further
demonstrating the SU(2) nature of the valley isospin in bilayer graphene. Our
experiment paves the path for future efforts of manipulating the valley isospin
in bilayer graphene to engineer exotic topological orders and quantum
information processes.Comment: 24 pages, 14 figure
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