71 research outputs found
Decision Tree Heuristics Can Fail, Even in the Smoothed Setting
Greedy decision tree learning heuristics are mainstays of machine learning practice, but theoretical justification for their empirical success remains elusive. In fact, it has long been known that there are simple target functions for which they fail badly (Kearns and Mansour, STOC 1996).
Recent work of Brutzkus, Daniely, and Malach (COLT 2020) considered the smoothed analysis model as a possible avenue towards resolving this disconnect. Within the smoothed setting and for targets f that are k-juntas, they showed that these heuristics successfully learn f with depth-k decision tree hypotheses. They conjectured that the same guarantee holds more generally for targets that are depth-k decision trees.
We provide a counterexample to this conjecture: we construct targets that are depth-k decision trees and show that even in the smoothed setting, these heuristics build trees of depth 2^{?(k)} before achieving high accuracy. We also show that the guarantees of Brutzkus et al. cannot extend to the agnostic setting: there are targets that are very close to k-juntas, for which these heuristics build trees of depth 2^{?(k)} before achieving high accuracy
Video Timeline Modeling For News Story Understanding
In this paper, we present a novel problem, namely video timeline modeling.
Our objective is to create a video-associated timeline from a set of videos
related to a specific topic, thereby facilitating the content and structure
understanding of the story being told. This problem has significant potential
in various real-world applications, such as news story summarization. To
bootstrap research in this area, we curate a realistic benchmark dataset,
YouTube-News-Timeline, consisting of over k timelines and k YouTube
news videos. Additionally, we propose a set of quantitative metrics as the
protocol to comprehensively evaluate and compare methodologies. With such a
testbed, we further develop and benchmark exploratory deep learning approaches
to tackle this problem. We anticipate that this exploratory work will pave the
way for further research in video timeline modeling. The assets are available
via
https://github.com/google-research/google-research/tree/master/video_timeline_modeling.Comment: Accepted as a spotlight by NeurIPS 2023, Track on Datasets and
Benchmark
High-performance chiral all-optical logic gate based on topological edge states of valley photonic crystal
For all-optical communication and information processing, it is necessary to
develop all-optical logic gates based on photonic structures that can directly
perform logic operations. All-optical logic gates have been demonstrated based
on conventional waveguides and interferometry, as well as photonic crystal
structures. Nonetheless, any defects in those structures will introduce high
scattering loss, which compromises the fidelity and contrast ratio of the
information process. Based on the spin-valley locking effect that can achieve
defect-immune unidirectional transmission of topological edge states in valley
photonic crystals (VPCs), we propose a high-performance all-optical logic OR
gate based on a VPC structure. By tuning the working bandwidth of the two input
channels, we prevent interference between the two channels to achieve a stable
and high-fidelity output. The transmittance of both channels is higher than
0.8, and a high contrast ratio of 28.8 dB is achieved. Moreover, the chirality
of the logic gate originated from the spin-valley locking effect allows using
different circularly polarized light as inputs, representing "1" or "0", which
is highly desired in quantum computing. The device's footprint is small,
allowing high-density on-chip integration. In addition, this design can be
experimentally fabricated using current nanofabrication techniques and will
have potential applications in optical communication, information processing,
and quantum computing.Comment: 10 pages, 6 figure
Topological Singularity Induced Chiral Kohn Anomaly in a Weyl Semimetal
The electron-phonon interaction (EPI) is instrumental in a wide variety of
phenomena in solid-state physics, such as electrical resistivity in metals,
carrier mobility, optical transition and polaron effects in semiconductors,
lifetime of hot carriers, transition temperature in BCS superconductors, and
even spin relaxation in diamond nitrogen-vacancy centers for quantum
information processing. However, due to the weak EPI strength, most phenomena
have focused on electronic properties rather than on phonon properties. One
prominent exception is the Kohn anomaly, where phonon softening can emerge when
the phonon wavevector nests the Fermi surface of metals. Here we report a new
class of Kohn anomaly in a topological Weyl semimetal (WSM), predicted by
field-theoretical calculations, and experimentally observed through inelastic
x-ray and neutron scattering on WSM tantalum phosphide (TaP). Compared to the
conventional Kohn anomaly, the Fermi surface in a WSM exhibits multiple
topological singularities of Weyl nodes, leading to a distinct nesting
condition with chiral selection, a power-law divergence, and non-negligible
dynamical effects. Our work brings the concept of Kohn anomaly into WSMs and
sheds light on elucidating the EPI mechanism in emergent topological materials.Comment: 30 pages, 4 main figures, 11 supplementary figures and 1 theoretical
derivation. Feedback most welcom
High Expressions of CUL4A and TP53 in Colorectal Cancer Predict Poor Survival
Background/Aims: Cullin 4A (CUL4A) is vital in cell survival, development, growth and cell cycle, it plays an important role in chaperone-mediated ubiquitination and interacts with TP53 in carcinogenesis. However, the clinicopathologic significance of CUL4A expression in colorectal cancer is unknown; in particular, the prognostic value of CUL4A combined with TP53 expression has not been explored. Methods: We analyzed the expression of CUL4A in both public database (Oncomine) and 180 cases of colorectal cancer and paired normal tissues by real-time polymerase chain reaction and western blotting. Colony formation, wound healing, migration and invasion assays and tumorigenesis in nude mice were used to explore the function of CUL4A in CRC proliferation and metastasis in vitro and in vivo. Markers of epithelial to mesenchymal transition (EMT) were evaluated by western blotting. Immunohistochemistry (IHC) was used to analyse the relationship between CUL4A expression and E-cadherin expression. Results: CUL4A and TP53 protein expression was significantly higher in cancerous tissues compared to normal tissues. Significant correlation between CUL4A and TP53 expression was observed. CUL4A expression was an independent prognostic factor for overall survival (OS) and disease-free survival (DFS). Interestingly, patients with tumors that had both CUL4A overexpression and mutant TP53 protein accumulation relapsed and died within a significantly short period after surgery (P < 0.001). Multivariate analysis showed that patients with both CUL4A+ and TP53+ positive tumors had extremely poor OS and DFS. Knockdown of CUL4A by a short interfering RNA (siRNA) significantly suppressed the progression of EMT, proliferation, migration, and invasion of colon cancer cells in vitro and tumor growth in vivo. ZEB1 silencing blocked CUL4A-driven these processes. Conclusion: CUL4A expression correlated positively with the prognosis of colorectal cancer. Mechanistically, ZEB1 was confirmed to mediate the function of CUL4A in regulating the EMT. The assessment of both CUL4A and mutant TP53 expression will be helpful in predicting colon cancer prognosis
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