5,450 research outputs found
Growth of Large Domain Epitaxial Graphene on the C-Face of SiC
Growth of epitaxial graphene on the C-face of SiC has been investigated.
Using a confinement controlled sublimation (CCS) method, we have achieved well
controlled growth and been able to observe propagation of uniform monolayer
graphene. Surface patterns uncover two important aspects of the growth, i.e.
carbon diffusion and stoichiometric requirement. Moreover, a new "stepdown"
growth mode has been discovered. Via this mode, monolayer graphene domains can
have an area of hundreds of square micrometers, while, most importantly, step
bunching is avoided and the initial uniformly stepped SiC surface is preserved.
The stepdown growth provides a possible route towards uniform epitaxial
graphene in wafer size without compromising the initial flat surface morphology
of SiC.Comment: 18 pages, 8 figure
A Short-Armed Troodontid Dinosaur from the Upper Cretaceous of Inner Mongolia and Its Implications for Troodontid Evolution
BACKGROUND: The Troodontidae represents one of the most bird-like theropod groups and plays an important role in our understanding of avian origins. Although troodontids have been known for over 150 years, few known derived troodontid specimens preserve significant portions of both the forelimb and the hindlimb. METHODOLOGY/PRINCIPAL FINDINGS: Here, we report a new troodontid taxon, Linhevenator tani gen. et sp. nov., based on a partial, semi-articulated skeleton recovered from the Upper Cretaceous Wulansuhai Formation of Wulatehouqi, Inner Mongolia, China. L. tani has an unusual combination of primitive and derived character states, though our phylogenetic analysis places it in a derived clade within the Troodontidae. As a derived taxon, L. tani has a dromaeosaurid-like pedal digit II, and this species also possesses a humerus that is proportionally much shorter and more robust than those of most other troodontids. CONCLUSION/SIGNIFICANCE: The combination of features present in Linhevenator indicates a complex pattern of character evolution within the Troodontidae. In particular, the discovery of Linhevenator suggests that derived troodontids have independently evolved a highly specialized pedal digit II and have significantly shortened the forelimb over the course of their evolution
Simulating the Kibble-Zurek mechanism of the Ising model with a superconducting qubit system
The Kibble-Zurek mechanism (KZM) predicts the density of topological defects
produced in the dynamical processes of phase transitions in systems ranging
from cosmology to condensed matter and quantum materials. The similarity
between KZM and the Landau-Zener transition (LZT), which is a standard tool to
describe the dynamics of some non-equilibrium physics in contemporary physics,
is being extensively exploited. Here we demonstrate the equivalence between KZM
in the Ising model and LZT in a superconducting qubit system. We develop a
time-resolved approach to study quantum dynamics of LZT with nano-second
resolution. By using this technique, we simulate the key features of KZM in the
Ising model with LZT, e.g., the boundary between the adiabatic and impulse
regions, the freeze-out phenomenon in the impulse region, especially, the
scaling law of the excited state population as the square root of the quenching
rate. Our results supply the experimental evidence of the close connection
between KZM and LZT, two textbook paradigms to study the dynamics of the
non-equilibrium phenomena.Comment: Title changed, authors added, and some experimental data update
Super resolution dual-layer CBCT imaging with model-guided deep learning
Objective: This study aims at investigating a novel super resolution CBCT
imaging technique with the dual-layer flat panel detector (DL-FPD). Approach:
In DL-FPD based CBCT imaging, the low-energy and high-energy projections
acquired from the top and bottom detector layers contain intrinsically
mismatched spatial information, from which super resolution CBCT images can be
generated. To explain, a simple mathematical model is established according to
the signal formation procedure in DL-FPD. Next, a dedicated recurrent neural
network (RNN), named as suRi-Net, is designed by referring to the above imaging
model to retrieve the high resolution dual-energy information. Different
phantom experiments are conducted to validate the performance of this newly
developed super resolution CBCT imaging method. Main Results: Results show that
the proposed suRi-Net can retrieve high spatial resolution information
accurately from the low-energy and high-energy projections having lower spatial
resolution. Quantitatively, the spatial resolution of the reconstructed CBCT
images of the top and bottom detector layers is increased by about 45% and 54%,
respectively. Significance: In future, suRi-Net provides a new approach to
achieve high spatial resolution dual-energy imaging in DL-FPD based CBCT
systems
Optimal Spatial Matrix Filter Design for Array Signal Preprocessing
An efficient technique of designing spatial matrix filter for array signal preprocessing based on convex programming was proposed. Five methods were considered for designing the filter. In design method 1, we minimized the passband fidelity subject to the controlled overall stopband attenuation level. In design method 2, the objective function and the constraint in the design method 1 were reversed. In design method 3, the optimal matrix filter which has the general mean square error was considered. In design method 4, the left stopband and the right stopband were constrained with specific attenuation level each, and the minimized passband fidelity was received. In design method 5, the optimization objective function was the sum of the left stopband and the right stopband attenuation levels with the weighting factors 1 and γ, respectively, and the passband fidelity was the constraints. The optimal solution of the optimizations above was derived by the Lagrange multiplier theory. The relations between the optimal solutions were analyzed. The generalized singular value decomposition was introduced to simplify the optimal solution of design methods 1 and 2 and enhanced the efficiency of solving the Lagrange multipliers. By simulations, it could be found that the proposed method was effective for designing the spatial matrix filter
Muscle 4EBP1 activation modifies the structure and function of the neuromuscular junction in mice
Dysregulation of mTOR complex 1 (mTORC1) activity drives neuromuscular junction (NMJ) structural instability during aging; however, downstream targets mediating this effect have not been elucidated. Here, we investigate the roles of two mTORC1 phosphorylation targets for mRNA translation, ribosome protein S6 kinase 1 (S6K1) and eukaryotic translation initiation factor 4E-binding protein 1 (4EBP1), in regulating NMJ structural instability induced by aging and sustained mTORC1 activation. While myofiber-specific deletion of S6k1 has no effect on NMJ structural integrity, 4EBP1 activation in murine muscle induces drastic morphological remodeling of the NMJ with enhancement of synaptic transmission. Mechanistically, structural modification of the NMJ is attributed to increased satellite cell activation and enhanced post-synaptic acetylcholine receptor (AChR) turnover upon 4EBP1 activation. Considering that loss of post-synaptic myonuclei and reduced NMJ turnover are features of aging, targeting 4EBP1 activation could induce NMJ renewal by expanding the pool of post-synaptic myonuclei as an alternative intervention to mitigate sarcopenia
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