Reducing Popularity Bias in Recommender Systems through AUC-Optimal Negative Sampling

Popularity bias is a persistent issue associated with recommendation systems, posing challenges to both fairness and efficiency. Existing literature widely acknowledges that reducing popularity bias often requires sacrificing recommendation accuracy. In this paper, we challenge this commonly held belief. Our analysis under general bias-variance decomposition framework shows that reducing bias can actually lead to improved model performance under certain conditions. To achieve this win-win situation, we propose to intervene in model training through negative sampling thereby modifying model predictions. Specifically, we provide an optimal negative sampling rule that maximizes partial AUC to preserve the accuracy of any given model, while correcting sample information and prior information to reduce popularity bias in a flexible and principled way. Our experimental results on real-world datasets demonstrate the superiority of our approach in improving recommendation performance and reducing popularity bias.Comment: 20 page

[meso-Tetra­kis(4-heptyl­oxyphen­yl)porphyrinato]nickel(II)

In the title compound, [Ni(C72H84N4O4)], the four-coordinate NiII ion in the middle of the planar 24-membered porphyrin ring is located on a crystallograpic inversion center, with Ni—N distances of 1.946 (2)–1.951 (2) Å. The 4-heptyl­oxyphenyl groups are twisted with respect to the porphyrin mean plane, the dihedral angles being 88.5 (3) and 79.1 (2)°

{5,10,15,20-Tetra­kis[4-(hex­yloxy)phen­yl]porphyrinato}nickel(II)

The mol­ecule of the title compound, [Ni(C68H76N4O4)], is located on a crystallographic inversion center. The Ni—N distances within the square-shaped coordination environment are 1.951 (2) and 1.954 (2) Å. Three terminal C atoms in one of the hexyl groups are disordered over two sets of sites, with site-occupancy factors of 0.615 (13) and 0.385 (13)

[(1,3-Benzothia­zol-2-yl)amino­carbon­yl]meth­yl piperidine-1-carbodithio­ate monohydrate

In the title compound, C15H17N3OS3·H2O, the piperidine ring has a chair conformation. The crystal structure is stabilized by weak inter­molecular N—H⋯O, O—H⋯N and O—H⋯O hydrogen-bonding inter­actions

One-Shot High-Fidelity Talking-Head Synthesis with Deformable Neural Radiance Field

Talking head generation aims to generate faces that maintain the identity information of the source image and imitate the motion of the driving image. Most pioneering methods rely primarily on 2D representations and thus will inevitably suffer from face distortion when large head rotations are encountered. Recent works instead employ explicit 3D structural representations or implicit neural rendering to improve performance under large pose changes. Nevertheless, the fidelity of identity and expression is not so desirable, especially for novel-view synthesis. In this paper, we propose HiDe-NeRF, which achieves high-fidelity and free-view talking-head synthesis. Drawing on the recently proposed Deformable Neural Radiance Fields, HiDe-NeRF represents the 3D dynamic scene into a canonical appearance field and an implicit deformation field, where the former comprises the canonical source face and the latter models the driving pose and expression. In particular, we improve fidelity from two aspects: (i) to enhance identity expressiveness, we design a generalized appearance module that leverages multi-scale volume features to preserve face shape and details; (ii) to improve expression preciseness, we propose a lightweight deformation module that explicitly decouples the pose and expression to enable precise expression modeling. Extensive experiments demonstrate that our proposed approach can generate better results than previous works. Project page: https://www.waytron.net/hidenerf/Comment: Accepted by CVPR 202

{5,10,15,20-Tetra­kis[4-(oct­yloxy)phen­yl]porphyrinato}copper(II)

In the title compound, [Cu(C76H92N4O4)], the central Cu(II) ion is situated on an inversion centre. The porphyrinate core exhibits a nearly planar conformation [maximum deviation = 0.027 (3) Å], with Cu—N distances of 1.997 (2) and 2.001 (2) Å. The benzene rings of the 4-octyloxyphenyl groups are rotated at angles of 84.02 (8) and 77.02 (6)° with respect to the mean plane of the porphyrin fragment. The two terminal C atoms in the octyl group are disordered over two positions of equal occupancy

{meso-Tetra­kis[p-(hept­yloxy)phen­yl]­porphyrinato}silver(II)

The title compound, [Ag(C72H84N4O4)], crystallizes with the AgII cation on a centre of symmetry. The macrocyclic 24-membered ring core is planar with a mean deviation of 0.0311 (15) Å and the four-coordinate AgII cation fits into its center, at 2.0814 (19) and 2.0872 (19) Å, from the surrounding pyrrole-N atoms, in agreement with what is found in related compounds. The p-heptyl­oxyphenyl groups are rotated 75.51 (5) and 84.45 (8)° with respect to the porphyrin mean plane, due to steric hindrance with the pyrrole-H atoms of the macrocycle