Observation of forbidden phonons and dark excitons by resonance Raman scattering in few-layer WS2_2

The optical properties of the two-dimensional (2D) crystals are dominated by tightly bound electron-hole pairs (excitons) and lattice vibration modes (phonons). The exciton-phonon interaction is fundamentally important to understand the optical properties of 2D materials and thus help develop emerging 2D crystal based optoelectronic devices. Here, we presented the excitonic resonant Raman scattering (RRS) spectra of few-layer WS$_2$ excited by 11 lasers lines covered all of A, B and C exciton transition energies at different sample temperatures from 4 to 300 K. As a result, we are not only able to probe the forbidden phonon modes unobserved in ordinary Raman scattering, but also can determine the bright and dark state fine structures of 1s A exciton. In particular, we also observed the quantum interference between low-energy discrete phonon and exciton continuum under resonant excitation. Our works pave a way to understand the exciton-phonon coupling and many-body effects in 2D materials.Comment: 14 pages, 11 figure

A method for estimation of critical stress intensity factor for welded sheet

Welded structures subjected to vibration loads in modern aerospace vehicles during practices have the hazard of undergoing fatigue. Critical stress intensity factor is the key parameter in the fatigue failure criterion. Usually fracture toughness is used as an approximation of the critical stress intensity factor in fatigue crack propagation calculation, however it can be seriously influenced by welding and thickness effects when applied to sheet metal welded joints. To solve the problem, this study analyzes these effects both experimentally and theoretically. The paper considers a method for estimation of the critical stress intensity factor based on crack size at the fatigue fracture location. Fatigue tests are conducted on welded specimens made of 2219-T87 aluminum alloy and critical stress intensity factors are calculated. The relationship for critical stress intensity factor results is determined from fracture crack sizes under different loading modes. Results reveal that the estimation method that was applied to measure the factor based on the fracture crack size excludes influences of welding and thickness effects in a convenient way of measurement and calculation. The method can be adopted for welded structures in spacecrafts subjected to vibration loads for fatigue failure analysis and reference of fracture toughness in engineering practice

1-(But-2-enyl­idene)-2-(2-nitro­phen­yl)hydrazine

The mol­ecule of the title Schiff base compound, C10H11N3O2, adopts an E geometry with respect to the C=N double bond. The mol­ecule is roughly planar, with the largest deviation from the mean plane being 0.111 (2) Å, The enyl­idene-hydrazine group is, however, slightly twisted with respect to the phenyl ring, making a dihedral angle of 6.5 (3)°. An intra­molecular N—H⋯O hydrogen bond may be responsible for the planar conformation. An inter­molecular N—H⋯O hydrogen bond links two mol­ecules around an inversion center, building a pseudo dimer

2-Eth­oxy-4-{[(2-nitro­phen­yl)hydrazono]meth­yl}phenol

The title compound, C15H15N3O4, a Schiff base, was obtained from a condensation reaction of 3-eth­oxy-4-hydroxy­benzaldehyde and 2-nitro­phenyl­hydrazine. The mol­ecule is approximately planar, the largest deviation from the mean plane being 0.1449 (16) Å. An intramolecular N—H⋯O inter­action is also present. In the crystal, inter­molecular O—H⋯O hydrogen bonds link the mol­ecules, forming chain parallel to the b axis

Dataset Condensation via Generative Model

Dataset condensation aims to condense a large dataset with a lot of training samples into a small set. Previous methods usually condense the dataset into the pixels format. However, it suffers from slow optimization speed and large number of parameters to be optimized. When increasing image resolutions and classes, the number of learnable parameters grows accordingly, prohibiting condensation methods from scaling up to large datasets with diverse classes. Moreover, the relations among condensed samples have been neglected and hence the feature distribution of condensed samples is often not diverse. To solve these problems, we propose to condense the dataset into another format, a generative model. Such a novel format allows for the condensation of large datasets because the size of the generative model remains relatively stable as the number of classes or image resolution increases. Furthermore, an intra-class and an inter-class loss are proposed to model the relation of condensed samples. Intra-class loss aims to create more diverse samples for each class by pushing each sample away from the others of the same class. Meanwhile, inter-class loss increases the discriminability of samples by widening the gap between the centers of different classes. Extensive comparisons with state-of-the-art methods and our ablation studies confirm the effectiveness of our method and its individual component. To our best knowledge, we are the first to successfully conduct condensation on ImageNet-1k.Comment: old work,done in 202