25 research outputs found
Learning with Noisy Labels Using Collaborative Sample Selection and Contrastive Semi-Supervised Learning
Learning with noisy labels (LNL) has been extensively studied, with existing
approaches typically following a framework that alternates between clean sample
selection and semi-supervised learning (SSL). However, this approach has a
limitation: the clean set selected by the Deep Neural Network (DNN) classifier,
trained through self-training, inevitably contains noisy samples. This mixture
of clean and noisy samples leads to misguidance in DNN training during SSL,
resulting in impaired generalization performance due to confirmation bias
caused by error accumulation in sample selection. To address this issue, we
propose a method called Collaborative Sample Selection (CSS), which leverages
the large-scale pre-trained model CLIP. CSS aims to remove the mixed noisy
samples from the identified clean set. We achieve this by training a
2-Dimensional Gaussian Mixture Model (2D-GMM) that combines the probabilities
from CLIP with the predictions from the DNN classifier. To further enhance the
adaptation of CLIP to LNL, we introduce a co-training mechanism with a
contrastive loss in semi-supervised learning. This allows us to jointly train
the prompt of CLIP and the DNN classifier, resulting in improved feature
representation, boosted classification performance of DNNs, and reciprocal
benefits to our Collaborative Sample Selection. By incorporating auxiliary
information from CLIP and utilizing prompt fine-tuning, we effectively
eliminate noisy samples from the clean set and mitigate confirmation bias
during training. Experimental results on multiple benchmark datasets
demonstrate the effectiveness of our proposed method in comparison with the
state-of-the-art approaches
Unusual activity of rationally designed cobalt phosphide/oxide heterostructure composite for hydrogen production in alkaline medium.
Design and development of an efficient, nonprecious catalyst with structural features and functionality necessary for driving the hydrogen evolution reaction (HER) in an alkaline medium remain a formidable challenge. At the root of the functional limitation is the inability to tune the active catalytic sites while overcoming the poor reaction kinetics observed under basic conditions. Herein, we report a facile approach to enable the selective design of an electrochemically efficient cobalt phosphide oxide composite catalyst on carbon cloth (CoP-CoxOy/CC), with good activity and durability toward HER in alkaline medium (η10= -43 mV). Theoretical studies revealed that the redistribution of electrons at laterally dispersed Co phosphide/oxide interfaces gives rise to a synergistic effect in the heterostructured composite, by which various Co oxide phases initiate the dissociation of the alkaline water molecule. Meanwhile, the highly active CoP further facilitates the adsorption-desorption process of water electrolysis, leading to extremely high HER activity
Unravelling surface and interfacial structures of a metal–organic framework by transmission electron microscopy
Metal-organic frameworks (MOFs) are crystalline porous materials with designable topology, porosity and functionality, having promising applications in gas storage and separation, ion conduction and catalysis. It is challenging to observe MOFs with transmission electron microscopy (TEM) due to the extreme instability of MOFs upon electron beam irradiation. Here, we use a direct-detection electron-counting camera to acquire TEM images of the MOF ZIF-8 with an ultralow dose of 4.1 electrons per square ångström to retain the structural integrity. The obtained image involves structural information transferred up to 2.1 Å, allowing the resolution of individual atomic columns of Zn and organic linkers in the framework. Furthermore, TEM reveals important local structural features of ZIF-8 crystals that cannot be identified by diffraction techniques, including armchair-type surface terminations and coherent interfaces between assembled crystals. These observations allow us to understand how ZIF-8 crystals self-assemble and the subsequent influence of interfacial cavities on mass transport of guest molecules
Realization of Self-Rotating Droplets Based on Liquid Metal
Owing to their fascinating characteristics, liquid metals (LMs) have attracted increasing attention from the scientific community, and are a potential material for various applications. A novel phenomenon is reported in which an acid droplet spontaneously rotates on the surface of an LM. The experimental results show that this phenomenon originates from the collective motion of bubbles generated by the chemical reactions between the droplet and the LM. The angular velocity of the droplet rotation is on the order of 10(1) rad s(-1), which is much higher than that driven by other mechanisms. Under different conditions, the period of the droplet differs, and it increases with the pH and radius of the acid droplet. The theoretical results indicate the dominant factors and the characterized angular velocity, which agree well with the experimental data. This phenomenon demonstrate that the general particles can also induce special spatial-temporal patterns, and opens up a new field for the application of LMs
Spontaneous Motion and Rotation of Acid Droplets on the Surface of a Liquid Metal
Self-propulsion of droplets is of great significance in many fields. The spontaneous horizontal motion and self-jumping of droplets have been well realized in various ways. However, there is still a lack of an effective method to enable a droplet to rotate spontaneously and steadily. In this paper, by employing an acid droplet and a liquid metal, the spontaneous and steady rotation of droplets is achieved. For an acid droplet, it may spontaneously move when it is deposited on the surface of the liquid metal. By adjusting experimental parameters to the proper range, the self-rotation of droplet happens. This phenomenon originates from the fluctuation of the droplet boundary and the collective movement of bubbles that are generated by the chemical reactions between the acid droplet and liquid metal. This rotation has a simpler implementation method and more steady rotation state. Its angular velocity is much higher than that driven by other mechanisms. Moreover, the movements of acid droplets on the liquid metal are classified according to experimental conditions. The internal flow fields, the movements and distribution of bubbles, and the fluctuation of the droplet boundary are also explored and discussed. The theoretical model describing the rotational droplet is given. Our work may deepen the understanding of the physical system transition affected by chemical reactions and provide a new way for the design of potential applications, e.g., micro- and nanodevices
Facile Synthesis of a Hydroxyl-Functionalized Tröger’s Base Diamine: A New Building Block for High-Performance Polyimide Gas Separation Membranes
Two intrinsically microporous polyimides
(PIM-PIs) were synthesized
by the polycondensation reaction of 4,4′-(hexafluoroisopropylidene)diphthalic
anhydride (6FDA) and 3,3,3′,3′-tetramethylspirobisindane-6,7,6′,7′-tetracarboxylic
dianhydride (SBI) with a newly designed <i>o</i>-hydroxyl-functionalized
Tröger’s base diamine, 1,7-diamino-6<i>H</i>,12<i>H</i>-5,11-methanodibenzo[1,5]diazocine-2,8-diol
(HTB). Both amorphous PIM-PIs were soluble in aprotic solvents and
showed excellent thermal stability with onset decomposition temperature
of ∼380 °C. SBI-HTB displayed a higher CO<sub>2</sub> permeability
(466 vs 67 barrer) than 6FDA-HTB but a significantly lower selectivity
for CO<sub>2</sub>/CH<sub>4</sub> (29 vs 73), H<sub>2</sub>/CH<sub>4</sub> (29 vs 181), O<sub>2</sub>/N<sub>2</sub> (4.6 vs 6.0), and
N<sub>2</sub>/CH<sub>4</sub> (1 vs 2.5). 6FDA-HTB displayed the highest
gas-pair permselectivity values of all reported OH-functionalized
PIM-PIs to date. The high permselectivity of 6FDA-HTB resulted primarily
from exceptional diffusion selectivity due to strong size-sieving
properties caused by hydrogen bonding between the proton of the hydroxyl
group and the nitrogen atoms in the tertiary amine of the Tröger’s
base (O–H···N)
Effect of ultrasonic pre-treatment on Ara h 1 in peanut sprouts
Ara h 1 is the most abundant sensitizing protein in peanuts; it has high thermal stability and is difficult to degrade. The peanut sprout is a high-quality, natural food that has various beneficial effects and lower allergenicity than peanut seeds. In this study, ultrasonication (US) of peanut sprouts was used to alter their Ara h 1 content. We determined that the optimal parameters for the US process were 35 °C temperature, 30 min duration, 240 W power, and 100 kHz frequency. After 5 days of germination, the protease activity of the control (blank) group increased to 262.39 ± 0.10 U, whereas that of the US group increased to 290.1 ± 0.25 U. We also investigated the effects of US on Ara h 1 protein composition, structure, and related gene expression during germination. ELISA results showed that after 5 days of germination, Ara h 1 content in the blank group decreased from 20.63 ± 0.31 ppm to 3.35 ± 0.42 ppm, whereas in the US group, they decreased to below the detection limit. SDS-PAGE bands between 50 and 70 kDa from peanut sprout extracts gradually became lighter in both groups. The band almost disappeared at day 5 of germination in the US group, indicating that US reduced the Ara h 1 content of peanut sprouts, consistent with the ELISA results. The expression of the Ara h 1 gene in peanut seeds was 173.92 ± 26.37. In the BK control group, it decreased to 0.49 ± 0.17 on the fourth day and increased slightly to 0.75 ± 0.09 on the fifth day. In the US group, it decreased to 1.37 ± 0.28 on the first day, dropped sharply to 0.00 on the third day, and increased slightly to 0.04 ± 0.01 on the fourth and fifth days. Protein structure results showed that the α-helix structure of Ara h 1 decreased after US, whereas the content of β-fold structures increased. The surface hydrophobicity decreased, and the secondary and tertiary structures of Ara h 1 were loose
Experimental evidence of chiral gold nanowires with boerdijk-coxeter-bernal structure by atomic-resolution imaging
Abstract is not available in fulltext.Published versio
One-Step Facile Synthesis of a Simple Hole Transport Material for Efficient Perovskite Solar Cells
A study was conducted to report a new, simple, hole transport material (HTM) composed of a central difluorinated phenyl ring, tetra-substituted with paramethoxydiarylamine groups (DFTAB). Devices fabricated using DFTAB demonstrated a stabilized PCE, had a higher energy absorption cutoff than devices utilizing the ubiquitous spiro-OMeTAD, and offered the potential to be used without the addition of ionic additives. The synthesis of DFTAB was carried out in a one pot reaction where 4,4'-dimethoxydiphenylamine was first deprotonated by NaH, followed by nucleophilic aromatic substitution of hexafluorobenzene with in situ generated amide sodium salt. The thermal properties were investigated by thermogravimetric analysis (TGA)