Intertwined dipolar and multipolar order in the triangular-lattice magnet TmMgGaO4_4

A phase transition is often accompanied by the appearance of an order parameter and symmetry breaking. Certain magnetic materials exhibit exotic hidden-order phases, in which the order parameters are not directly accessible to conventional magnetic measurements. Thus, experimental identification and theoretical understanding of a hidden order are difficult. Here we combine neutron scattering and thermodynamic probes to study the newly discovered rare-earth triangular-lattice magnet TmMgGaO$_4$. Clear magnetic Bragg peaks at K points are observed in the elastic neutron diffraction measurements. More interesting, however, is the observation of sharp and highly dispersive spin excitations that cannot be explained by a magnetic dipolar order, but instead is the direct consequence of the underlying multipolar order that is "hidden" in the neutron diffraction experiments. We demonstrate that the observed unusual spin correlations and thermodynamics can be accurately described by a transverse field Ising model on the triangular lattice with an intertwined dipolar and ferro-multipolar order.Comment: Published versio

Bis(μ-2-phenyl­quinoline-4-carboxyl­ato)-κ3 O,O′:O;κ3 O:O,O′-bis­[(2,2′-bipyridine-κ2 N,N′)(2-phenyl­quinoline-4-carboxyl­ato-κ2 O,O′)cadmium(II)]

The neutral binuclear title complex, [Cd2(C16H10NO2)4(C10H8N2)2], is centrosymmetric, with the inversion center generating the central (μ-O)2Cd2 bridge. The CdII ion is in a strongly distorted CdN2O5 penta­gonal-bipyramidal geometry, defined by two N atoms from one 2,2′-bipyridine ligand and five O atoms from three 2-phenyl­quinoline-4-carboxyl­ate ligands, one monodentate, two bidentate. Weak inter­molecular π–π inter­actions [centroid–centroid distance = 3.712 (3) Å] help to establish the packing of the structure

Towards Stable Backdoor Purification through Feature Shift Tuning

It has been widely observed that deep neural networks (DNN) are vulnerable to backdoor attacks where attackers could manipulate the model behavior maliciously by tampering with a small set of training samples. Although a line of defense methods is proposed to mitigate this threat, they either require complicated modifications to the training process or heavily rely on the specific model architecture, which makes them hard to deploy into real-world applications. Therefore, in this paper, we instead start with fine-tuning, one of the most common and easy-to-deploy backdoor defenses, through comprehensive evaluations against diverse attack scenarios. Observations made through initial experiments show that in contrast to the promising defensive results on high poisoning rates, vanilla tuning methods completely fail at low poisoning rate scenarios. Our analysis shows that with the low poisoning rate, the entanglement between backdoor and clean features undermines the effect of tuning-based defenses. Therefore, it is necessary to disentangle the backdoor and clean features in order to improve backdoor purification. To address this, we introduce Feature Shift Tuning (FST), a method for tuning-based backdoor purification. Specifically, FST encourages feature shifts by actively deviating the classifier weights from the originally compromised weights. Extensive experiments demonstrate that our FST provides consistently stable performance under different attack settings. Without complex parameter adjustments, FST also achieves much lower tuning costs, only 10 epochs. Our codes are available at https://github.com/AISafety-HKUST/stable_backdoor_purification.Comment: NeurIPS 2023 paper. The first two authors contributed equall

The Power Spectra of Two Classes of Long-duration Gamma-ray Bursts

We have studied the averaged power density spectra (PDSs) of two classes of long-duration gamma-ray bursts in the recent classification by Balastegui et al.(2001) based on neural network analysis. Both PDSs follow a power law over a wide frequency range with approximately the same slope, which indicates that a process with a self-similar temporal property may underlie the emission mechanisms of both. The two classes of bursts are divided into groups according to their brightness and spectral hardness respectively and each group's PDS was calculated; For both classes, the PDS is found to flatten both with increasing burst brightness and with increasing hardness.Comment: 6 pages, 3 figures, a translated version from published in the Acta Astronomica Sinica, to appear in the Chinese Astronomy & Astrophysics Vol.27, Issue

Kinked linear response from non-Hermitian pumping

Non-Hermiticity is known to give rise to modified topological bulk-boundary correspondences, which predict the presence of topological boundary modes through appropriately modified topological invariants. Yet, little is currently known about how non-Hermiticity affects the precise linear response of wavepackets beyond their overall spectral flow. In this work, we discover that generically, non-Hermiticity gives rise to abrupt and prominent kinks in the semi-classical wavepacket trajectories of quantum gases, despite the absence of sudden physical impulses. This physically stems from a hitherto under-appreciated intrinsic non-locality from non-Hermitian pumping, even if all physical couplings are local, thereby resulting in enigmatic singularities in the band structure that lead to discontinuous band geometry and Berry curvature. For concrete experimental demonstration, we propose an ultracold atomic setup in a two-dimensional optical lattice with laser-induced loss, such that response kinks can be observed without fine-tuning in the physical atomic cloud dynamics. Our results showcases unique non-monotonic behavior from non-Hermitian pumping beyond the non-Hermitian skin effect, and suggests new avenues for investigating non-Hermitian dynamics in ultracold atomic platforms.Comment: 21 pages, 7 figure

Integrated Genomic and Proteomic Analyses of High-level Chloramphenicol Resistance in Campylobacter jejuni

Campylobacter jejuni is a major zoonotic pathogen, and its resistance to antibiotics is of great concern for public health. However, few studies have investigated the global changes of the entire organism with respect to antibiotic resistance. Here, we provide mechanistic insights into high-level resistance to chloramphenicol in C. jejuni, using integrated genomic and proteomic analyses. We identified 27 single nucleotide polymorphisms (SNPs) as well as an efflux pump cmeBmutation that conferred modest resistance. We determined two radical S-adenosylmethionine (SAM) enzymes, one each from an SNP gene and a differentially expressed protein. Validation of major metabolic pathways demonstrated alterations in oxidative phosphorylation and ABC transporters, suggesting energy accumulation and increase in methionine import. Collectively, our data revealed a novel rRNA methylation mechanism by a radical SAM superfamily enzyme, indicating that two resistance mechanisms existed in Campylobacter. This work provided a systems biology perspective on understanding the antibiotic resistance mechanisms in bacteria