2,653 research outputs found
A-priori Validation of Subgrid-scale Models for Astrophysical Turbulence
We perform a-priori validation tests of subgrid-scale (SGS) models for the
turbulent transport of momentum, energy and passive scalars. To this end, we
conduct two sets of high-resolution hydrodynamical simulations with a
Lagrangian code: an isothermal turbulent box with rms Mach number of 0.3, 2 and
8, and the classical wind tunnel where a cold cloud traveling through a hot
medium gradually dissolves due to fluid instabilities. Two SGS models are
examined: the eddy diffusivity (ED) model wildly adopted in astrophysical
simulations and the "gradient model" due to Clark et al. (1979). We find that
both models predict the magnitude of the SGS terms equally well (correlation
coefficient > 0.8). However, the gradient model provides excellent predictions
on the orientation and shape of the SGS terms while the ED model predicts
poorly on both, indicating that isotropic diffusion is a poor approximation of
the instantaneous turbulent transport. The best-fit coefficient of the gradient
model is in the range of [0.16, 0.21] for the momentum transport, and the
turbulent Schmidt number and Prandtl number are both close to unity, in the
range of [0.92, 1.15].Comment: ApJ accepted; analysis code available at
https://github.com/huchiayu/Lapriori.j
A Semi-Automated Approach to Medical Image Segmentation using Conditional Random Field Inference
Medical image segmentation plays a crucial role in delivering effective patient care in various diagnostic and treatment modalities. Manual delineation of target volumes and all critical structures is a very tedious and highly time-consuming process and introduce uncertainties of treatment outcomes of patients. Fully automatic methods holds great promise for reducing cost and time, while at the same time improving accuracy and eliminating expert variability, yet there are still great challenges. Legally and ethically, human oversight must be integrated with ”smart tools” favoring a semi-automatic technique which can leverage the best aspects of both human and computer.
In this work we show that we can formulate a semi-automatic framework for the segmentation problem by formulating it as an energy minimization problem in Conditional Random Field (CRF). We show that human input can be used as adaptive training data to condition a probabilistic boundary term modeled for the heterogeneous boundary characteristics of anatomical structures. We demonstrated that our method can effortlessly adapt to multiple structures and image modalities using a single CRF framework and tools to learn probabilistic terms interactively. To tackle a more difficult multi-class segmentation problem, we developed a new ensemble one-vs-rest graph cut algorithm. Each graph in the ensemble performs a simple and efficient bi-class (a target class vs the rest of the classes) segmentation. The final segmentation is obtained by majority vote. Our algorithm is both faster and more accurate when compared with the prior multi-class method which iteratively swaps classes. In this Thesis, we also include novel volumetric segmentation algorithms which employ deep learning and indicate how to synthesize our CRF framework with convolutional neural networks (CNN). This would allow incorporating user guidance into CNN based deep learning for this task. We think a deep learning based method interactively guided by human expert is the ideal solution for medical image segmentation
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Surface-immobilised micelles via cucurbit[8]uril-rotaxanes for solvent-induced burst release.
The fabrication, characterisation and controlled burst release of naphthol-functionalised micellar (NFM) nanostructures, which were grafted onto gold surfaces through cucurbit[8]uril (CB[8]) mediated host-guest interactions are described. NFMs undergo a facile change in morphology from micelles to diblock copolymers in direct response to exposure to organic solvents, including tetrahydrofuran (THF), toluene and chloroform. This induced transition in conformation lends itself to potential applications including nanocarriers for triggered burst-release of guest molecules. Nile Red was investigated as a NFM encapsulated model hydrophobic cargo inside the surface-attached micelles, which could be fully released upon exposure to THF as measured by both atomic force microscopy and UV/vis spectroscopy.C. Hu thanks BP for supporting this work and Hughes Hall
College Cambridge for a student scholarship. Y. Zheng was
supported by an ERC starting investigator grant (ASPiRe
240629). Z. Yu is supported by an EPSRC grant (EP/H046593/1).This is the final version. It first appeared at http://pubs.rsc.org/en/Content/ArticleLanding/2015/CC/C5CC00121H#!divAbstract
Instance Neural Radiance Field
This paper presents one of the first learning-based NeRF 3D instance
segmentation pipelines, dubbed as Instance Neural Radiance Field, or Instance
NeRF. Taking a NeRF pretrained from multi-view RGB images as input, Instance
NeRF can learn 3D instance segmentation of a given scene, represented as an
instance field component of the NeRF model. To this end, we adopt a 3D
proposal-based mask prediction network on the sampled volumetric features from
NeRF, which generates discrete 3D instance masks. The coarse 3D mask prediction
is then projected to image space to match 2D segmentation masks from different
views generated by existing panoptic segmentation models, which are used to
supervise the training of the instance field. Notably, beyond generating
consistent 2D segmentation maps from novel views, Instance NeRF can query
instance information at any 3D point, which greatly enhances NeRF object
segmentation and manipulation. Our method is also one of the first to achieve
such results without ground-truth instance information during inference.
Experimented on synthetic and real-world NeRF datasets with complex indoor
scenes, Instance NeRF surpasses previous NeRF segmentation works and
competitive 2D segmentation methods in segmentation performance on unseen
views. See the demo video at https://youtu.be/wW9Bme73coI
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