212 research outputs found
Numerical investigation on aggregate settlement and its effect on the durability of hardened concrete
Vibrating consolidation process is widely applied to field construction of cement concrete. However, high-frequency vibration can easily lead to the settlement of coarse aggregates (CAs) and then affects the durability of hardened concrete. This study has developed a 3-D concrete model to investigate the CA settlement caused by vibration and its effect on long-term chloride transport in concrete. Based on the proposed model, the influence mechanism of CA settlement on both chloride concentration distribution and initiation time of reinforcement corrosion is discussed in detail. The results indicate that due to the settlement, a more obvious fluctuation of chloride concentration along the height direction of concrete specimen can be observed with the increase of vibration time. According to the model prediction, the corrosion of the top steel bar initiates 1.03–1.80 years earlier than that of the bottom steel bar under different vibration time. The proposed model provides a new method to probe into the influence of vibration-induced settlement on chloride ingress in hardened concrete
Stock market trading volumes and economic uncertainty dependence: before and during Sino-U.S. trade friction
This article mainly studies the interaction between the economic
uncertainty and stock market trading volumes changes before
and during Sino-U.S. trade friction using multifractal detrended
fluctuation analysis (M.F.-D.F.A.) and multifractal detrended crosscorrelation
analysis (M.F.-D.C.C.A.). Our research aims to reveal
whether the economic uncertainty increased by Sino-U.S. trade
friction affects stock market trading volume more susceptible, as
well as how policymaker strengthen risk management and maintain
financial stability. The results show that the dynamic volatility
linkages between economic uncertainty and stock market trading
volumes changes are multifractal, and the cross-correlation of
volatility linkages are anti-persistent. Through the rolling-windows
analysis, we also find that the economic uncertainty and trading
volumes are anti-persistent dynamic cross-correlated. This means
that while economic uncertainty increases, trading volume
decreases. Besides, Sino-U.S. trade friction has impact on the
cross-correlated behaviour significantly, suggesting that stock
markets’ risks are relatively large and trading volumes changes
are more susceptible by economic uncertainty during Sino-U.S.
trade friction in the U.S. Our study complements existing literature
about the stock markets trading volumes and economic
uncertainty dependence relationship by multifractal theory’s
methods. The overall findings imply that the increased economic
uncertainty caused by Sino-U.S. trade friction exacerbates financial
risks, which are useful for policymakers and investors
Uncertainty quantification for nonconvex tensor completion: Confidence intervals, heteroscedasticity and optimality
We study the distribution and uncertainty of nonconvex optimization for noisy
tensor completion -- the problem of estimating a low-rank tensor given
incomplete and corrupted observations of its entries. Focusing on a two-stage
estimation algorithm proposed by Cai et al. (2019), we characterize the
distribution of this nonconvex estimator down to fine scales. This
distributional theory in turn allows one to construct valid and short
confidence intervals for both the unseen tensor entries and the unknown tensor
factors. The proposed inferential procedure enjoys several important features:
(1) it is fully adaptive to noise heteroscedasticity, and (2) it is data-driven
and automatically adapts to unknown noise distributions. Furthermore, our
findings unveil the statistical optimality of nonconvex tensor completion: it
attains un-improvable accuracy -- including both the rates and the
pre-constants -- when estimating both the unknown tensor and the underlying
tensor factors.Comment: Accepted in part to ICML 202
Nonconvex Low-Rank Tensor Completion from Noisy Data
We study a noisy tensor completion problem of broad practical interest,
namely, the reconstruction of a low-rank tensor from highly incomplete and
randomly corrupted observations of its entries. While a variety of prior work
has been dedicated to this problem, prior algorithms either are computationally
too expensive for large-scale applications, or come with sub-optimal
statistical guarantees. Focusing on "incoherent" and well-conditioned tensors
of a constant CP rank, we propose a two-stage nonconvex algorithm -- (vanilla)
gradient descent following a rough initialization -- that achieves the best of
both worlds. Specifically, the proposed nonconvex algorithm faithfully
completes the tensor and retrieves all individual tensor factors within nearly
linear time, while at the same time enjoying near-optimal statistical
guarantees (i.e. minimal sample complexity and optimal estimation accuracy).
The estimation errors are evenly spread out across all entries, thus achieving
optimal statistical accuracy. We have also discussed how to
extend our approach to accommodate asymmetric tensors. The insight conveyed
through our analysis of nonconvex optimization might have implications for
other tensor estimation problems.Comment: Accepted to Operations Researc
Minimax Estimation of Linear Functions of Eigenvectors in the Face of Small Eigen-Gaps
Eigenvector perturbation analysis plays a vital role in various data science
applications. A large body of prior works, however, focused on establishing
eigenvector perturbation bounds, which are often highly inadequate
in addressing tasks that rely on fine-grained behavior of an eigenvector. This
paper makes progress on this by studying the perturbation of linear functions
of an unknown eigenvector. Focusing on two fundamental problems -- matrix
denoising and principal component analysis -- in the presence of Gaussian
noise, we develop a suite of statistical theory that characterizes the
perturbation of arbitrary linear functions of an unknown eigenvector. In order
to mitigate a non-negligible bias issue inherent to the natural ``plug-in''
estimator, we develop de-biased estimators that (1) achieve minimax lower
bounds for a family of scenarios (modulo some logarithmic factor), and (2) can
be computed in a data-driven manner without sample splitting. Noteworthily, the
proposed estimators are nearly minimax optimal even when the associated
eigen-gap is {\em substantially smaller} than what is required in prior
statistical theory
Binarized Spectral Compressive Imaging
Existing deep learning models for hyperspectral image (HSI) reconstruction
achieve good performance but require powerful hardwares with enormous memory
and computational resources. Consequently, these methods can hardly be deployed
on resource-limited mobile devices. In this paper, we propose a novel method,
Binarized Spectral-Redistribution Network (BiSRNet), for efficient and
practical HSI restoration from compressed measurement in snapshot compressive
imaging (SCI) systems. Firstly, we redesign a compact and easy-to-deploy base
model to be binarized. Then we present the basic unit, Binarized
Spectral-Redistribution Convolution (BiSR-Conv). BiSR-Conv can adaptively
redistribute the HSI representations before binarizing activation and uses a
scalable hyperbolic tangent function to closer approximate the Sign function in
backpropagation. Based on our BiSR-Conv, we customize four binarized
convolutional modules to address the dimension mismatch and propagate
full-precision information throughout the whole network. Finally, our BiSRNet
is derived by using the proposed techniques to binarize the base model.
Comprehensive quantitative and qualitative experiments manifest that our
proposed BiSRNet outperforms state-of-the-art binarization methods and achieves
comparable performance with full-precision algorithms. Code and models are
publicly available at https://github.com/caiyuanhao1998/BiSCI and
https://github.com/caiyuanhao1998/MSTComment: NeurIPS 2023; The first work to study binarized spectral compressive
imaging reconstruction proble
Increased expression of Gremlin1 promotes proliferation and epithelial mesenchymal transition in gastric cancer cells and correlates with poor prognosis of patients with gastric cancer
Background/Aim: Gremlin1 (GREM1) plays an important role in certain malignancies by antagonising bone morphogenetic proteins and regulating angiogenesis directly/indirectly. The present study aimed to investigate the role of Gremlin1 in the development and progression of gastric cancer (GC). Materials and Methods: Expression of GREM1 in GCs was examined using quantitative real time PCR and The Cancer Genomic Atlas (TCGA) data. Influence on cellular functions was determined in both Gremlin1 knockdown and overexpression cell line models. Results: GREM1 expression was up-regulated in GCs, which was correlated with poorer survival. Increased GREM1 expression was significantly correlated with tumour growth/invasion and lymphatic metastasis. Gremlin1 promoted proliferation and tumourigenic capacity of GC cells in vitro. GREM1 expression was associated with epithelial mesenchymal transition (EMT), angiogenesis and lymphangiogenesis in GC. Conclusion: Increased GREM1 expression in GCs is associated with disease progression and poor prognosis in which EMT, angiogenesis and lymphangiogenesis are likely involved
Persistent organic pollutants in ocean sediments from the North Pacific to the Arctic Ocean
Concentrations of polychlorinated biphenyls (PCBs), organochlorine pesticides (OC pesticides), and polybrominated diphenyl ethers (PBDEs) are reported in surficial sediments sampled along cruise transects from the Bering Sea to the central Arctic Ocean. OCs and PCBs all had significantly higher concentrations in the relatively shallow water (500 m) of the Bering Sea and Arctic Ocean (e.g., Canada Basin ΣPCB 149 ± 102 pg g−1 dw). Concentrations were similar to, or slightly lower than, studies from the 1990s, indicating a lack of a declining trend. PBDEs (excluding BDE-209) displayed very low concentrations (e.g., range of median values, 3.5–6.6 pg/g dw). In the shelf areas, the sediments comprised similar proportions of silt and clay, whereas the deep basin sediments were dominated by clay, with a lower total organic carbon (TOC) content. While significant positive correlations were observed between persistent organic pollutant (POP) concentrations and TOC (Pearson correlation, r = 0.66–0.75, p <0.05), the lack of strong correlations, combined with differing chemical profiles between the sediments and technical formulations (and/or marine surface waters), indicate substantial chemical processing during transfer to the benthic environment. Marked differences in sedimentation rates between the shallow and deeper water regions are apparent (the ∼5 cm-depth grab samples collected here representing ∼100 years of accumulation for the shelf sediments and ∼1000 years for the deeper ocean regions), which may bias any comparisons. Nonetheless, the sediments of the shallower coastal arctic seas appear to serve as significant repositories for POPs deposited from surface waters
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