642 research outputs found
A posteriori error bounds for the block-Lanczos method for matrix function approximation
We extend the error bounds from [SIMAX, Vol. 43, Iss. 2, pp. 787-811 (2022)]
for the Lanczos method for matrix function approximation to the block
algorithm. Numerical experiments suggest that our bounds are fairly robust to
changing block size and have the potential for use as a practical stopping
criteria. Further experiments work towards a better understanding of how
certain hyperparameters should be chosen in order to maximize the quality of
the error bounds, even in the previously studied block-size one case
SpinView: General Interactive Visual Analysis Tool for Multiscale Computational Magnetism
Multiscale magnetic simulations, including micromagnetic and atomistic spin
dynamics simulations, are widely used in the study of complex magnetic systems
over a wide range of spatial and temporal scales. The advances in these
simulation technologies have generated considerable amounts of data. However, a
versatile and general tool for visualization, filtering, and denoising this
data is largely lacking. To overcome these limitations, we have developed
SpinView, a general interactive visual analysis tool for graphical exploration
and data distillation. Combined with dynamic filters and a built-in database,
it is possible to generate reproducible publication-quality images, videos, or
portable interactive webpages within seconds. Since the basic input to SpinView
is a vector field, it can be directly integrated with any spin dynamics
simulation tool. With minimal effort on the part of the user, SpinView delivers
a simplified workflow, speeds up analysis of complex datasets and trajectories,
and enables new types of analysis and insight. SpinView is available from
https://mxjk851.github.io/SpinView
Deformer: Dynamic Fusion Transformer for Robust Hand Pose Estimation
Accurately estimating 3D hand pose is crucial for understanding how humans
interact with the world. Despite remarkable progress, existing methods often
struggle to generate plausible hand poses when the hand is heavily occluded or
blurred. In videos, the movements of the hand allow us to observe various parts
of the hand that may be occluded or blurred in a single frame. To adaptively
leverage the visual clue before and after the occlusion or blurring for robust
hand pose estimation, we propose the Deformer: a framework that implicitly
reasons about the relationship between hand parts within the same image
(spatial dimension) and different timesteps (temporal dimension). We show that
a naive application of the transformer self-attention mechanism is not
sufficient because motion blur or occlusions in certain frames can lead to
heavily distorted hand features and generate imprecise keys and queries. To
address this challenge, we incorporate a Dynamic Fusion Module into Deformer,
which predicts the deformation of the hand and warps the hand mesh predictions
from nearby frames to explicitly support the current frame estimation.
Furthermore, we have observed that errors are unevenly distributed across
different hand parts, with vertices around fingertips having disproportionately
higher errors than those around the palm. We mitigate this issue by introducing
a new loss function called maxMSE that automatically adjusts the weight of
every vertex to focus the model on critical hand parts. Extensive experiments
show that our method significantly outperforms state-of-the-art methods by 10%,
and is more robust to occlusions (over 14%).Comment: In ICCV 2023. Project: https://fuqichen1998.github.io/Deformer
Genetic-tunneling driven energy optimizer for spin systems
A long-standing and difficult problem in, e.g., condensed matter physics is
how to find the ground state of a complex many-body system where the potential
energy surface has a large number of local minima. Spin systems containing
complex and/or topological textures, for example spin spirals or magnetic
skyrmions, are prime examples of such systems. We propose here a
genetic-tunneling-driven variance-controlled optimization approach, and apply
it to two-dimensional magnetic skyrmionic systems. The approach combines a
local energy-minimizer backend and a metaheuristic global search frontend. The
algorithm is naturally concurrent, resulting in short user execution time. We
find that the method performs significantly better than simulated annealing
(SA). Specifically, we demonstrate that for the Pd/Fe/Ir(111) system, our
method correctly and efficiently identifies the experimentally observed spin
spiral, skyrmion lattice and ferromagnetic ground states as a function of
external magnetic field. To our knowledge, no other optimization method has
until now succeeded in doing this. We envision that our findings will pave the
way for evolutionary computing in mapping out phase diagrams for spin systems
in general
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Auxin response factor 6A regulates photosynthesis, sugar accumulation, and fruit development in tomato.
Auxin response factors (ARFs) are involved in auxin-mediated transcriptional regulation in plants. In this study, we performed functional characterization of SlARF6A in tomato. SlARF6A is located in the nucleus and exhibits transcriptional activator activity. Overexpression of SlARF6A increased chlorophyll contents in the fruits and leaves of tomato plants, whereas downregulation of SlARF6A decreased chlorophyll contents compared with those of wild-type (WT) plants. Analysis of chloroplasts using transmission electron microscopy indicated increased sizes of chloroplasts in SlARF6A-overexpressing plants and decreased numbers of chloroplasts in SlARF6A-downregulated plants. Overexpression of SlARF6A increased the photosynthesis rate and accumulation of starch and soluble sugars, whereas knockdown of SlARF6A resulted in opposite phenotypes in tomato leaves and fruits. RNA-sequence analysis showed that regulation of SlARF6A expression altered the expression of genes involved in chlorophyll metabolism, photosynthesis and sugar metabolism. SlARF6A directly bound to the promoters of SlGLK1, CAB, and RbcS genes and positively regulated the expression of these genes. Overexpression of SlARF6A also inhibited fruit ripening and ethylene production, whereas downregulation of SlARF6A increased fruit ripening and ethylene production. SlARF6A directly bound to the SAMS1 promoter and negatively regulated SAMS1 expression. Taken together, these results expand our understanding of ARFs with regard to photosynthesis, sugar accumulation and fruit development and provide a potential target for genetic engineering to improve fruit nutrition in horticulture crops
Design of 2D Skyrmionic Metamaterial Through Controlled Assembly
Despite extensive research on magnetic skyrmions and antiskyrmions, a
significant challenge remains in crafting nontrivial high-order skyrmionic
textures with varying, or even tailor-made, topologies. We address this
challenge, by focusing on a construction pathway of skyrmionics metamaterial
within a monolayer thin film and suggest several promising lattice-like,
flakes-like, and cell-like skyrmionic metamaterials that are surprisingly
stable. Central to our approach is the concept of 'simulated controlled
assembly', in short, a protocol inspired by 'click chemistry' that allows for
positioning topological magnetic structures where one likes, and then allowing
for energy minimization to elucidate the stability. Utilizing high-throughput
atomistic-spin-dynamic (ASD) simulations alongside state-of-the-art AI-driven
tools, we have isolated skyrmions (topological charge Q=1), antiskyrmions
(Q=-1), and skyrmionium (Q=0). These entities serve as foundational 'skyrmionic
building blocks' to forming reported intricate textures. In this work, two key
contributions are introduced to the field of skyrmionic systems. First, we
present a novel method for integrating control assembly protocols for the
stabilization and investigation of topological magnets, which marks a
significant advancement in the ability to explore new skyrmionic textures.
Second, we report on the discovery of skyrmionic metamaterials, which shows a
plethora of complex topologies that are possible to investigate theoretically
and experimentally
Metaheuristic conditional neural network for harvesting skyrmionic metastable states
We present a metaheuristic conditional neural-network-based method aimed at
identifying physically interesting metastable states in a potential energy
surface of high rugosity. To demonstrate how this method works, we identify and
analyze spin textures with topological charge ranging from 1 to
(where antiskyrmions have ) in the Pd/Fe/Ir(111) system, which we model
using a classical atomistic spin Hamiltonian based on parameters computed from
density functional theory. To facilitate the harvest of relevant spin textures,
we make use of the newly developed Segment Anything Model (SAM). Spin textures
with ranging from to are further analyzed using
finite-temperature spin-dynamics simulations. We observe that for temperatures
up to around 20\,K, lifetimes longer than 200\,ps are predicted, and that when
these textures decay, new topological spin textures are formed. We also find
that the relative stability of the spin textures depend linearly on the
topological charge, but only when comparing the most stable antiskyrmions for
each topological charge. In general, the number of holes (i.e.,
non-self-intersecting curves that define closed domain walls in the structure)
in the spin texture is an important predictor of stability -- the more holes,
the less stable is the texture. Methods for systematic identification and
characterization of complex metastable skyrmionic textures -- such as the one
demonstrated here -- are highly relevant for advancements in the field of
topological spintronics
Tuning skyrmions in B20 compounds by 4d and 5d doping
Skyrmion stabilization in novel magnetic systems with the B20 crystal
structure is reported here, primarily based on theoretical results. The focus
is on the effect of alloying on the 3d sublattice of the B20 structure by
substitution of heavier 4d and 5d elements, with the ambition to tune the
spin-orbit coupling and its influence on magnetic interactions.
State-of-the-art methods based on density functional theory are used to
calculate both isotropic and anisotropic exchange interactions. Significant
enhancement of the Dzyaloshinskii-Moriya interaction is reported for 5d-doped
FeSi and CoSi, accompanied by a large modification of the spin stiffness and
spiralization. Micromagnetic simulations coupled to atomistic spin-dynamics and
ab initio magnetic interactions reveal a helical ground state and field-induced
skyrmions for all these systems. Especially small skyrmions 50 nm are
predicted for CoOsSi, compared to 148 nm for
FeCoSi. Convex-hull analysis suggests that all B20 compounds
considered here are structurally stable at elevated temperatures and should be
possible to synthesize. This prediction is confirmed experimentally by
synthesis and structural analysis of the Ru-doped CoSi systems discussed here,
both in powder and in single-crystal forms.Comment: 18 pages, 21 figures, 9 table
Induction of Mycobacterium Tuberculosis Lipid-Specific T Cell Responses by Pulmonary Delivery of Mycolic Acid-Loaded Polymeric Micellar Nanocarriers
Mycolic acid (MA), a major lipid component of Mycobacterium tuberculosis (Mtb) cell wall, can be presented by the non-polymorphic antigen presenting molecule CD1b to T cells isolated from Mtb-infected individuals. These MA-specific CD1b-restricted T cells are cytotoxic, produce Th1 cytokines, and form memory populations, suggesting that MA can be explored as a potential subunit vaccine candidate for TB. However, the controlled elicitation of MA-specific T cell responses has been challenging due to difficulties in the targeted delivery of lipid antigens and a lack of suitable animal models. In this study, we generated MA-loaded micellar nanocarriers (MA-Mc) comprised of self-assembled poly(ethylene glycol)-bl-poly(propylene sulfide; PEG-PPS) copolymers conjugated to an acid sensitive fluorophore to enhance intracellular delivery of MA to phagocytic immune cells. Using humanized CD1 transgenic (hCD1Tg) mice, we found these nanobiomaterials to be endocytosed by bone marrow-derived dendritic cells (DCs) and localized to lysosomal compartments. Additionally, MA-Mc demonstrated superior efficacy over free MA in activating MA-specific TCR transgenic (DN1) T cells in vitro. Following intranasal immunization, MA-Mc were primarily taken up by alveolar macrophages and DCs in the lung and induced activation and proliferation of adoptively transferred DN1 T cells. Furthermore, intranasal immunization with MA-Mc induced MA-specific T cell responses in the lungs of hCD1Tg mice. Collectively, our data demonstrates that pulmonary delivery of MA via PEG-PPS micelles to DCs can elicit potent CD1b-restricted T cell responses both in vitro and in vivo and MA-Mc could be explored as subunit vaccines against Mtb infection
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