Collaborative Filtering with Social Exposure: A Modular Approach to Social Recommendation

This paper is concerned with how to make efficient use of social information to improve recommendations. Most existing social recommender systems assume people share similar preferences with their social friends. Which, however, may not hold true due to various motivations of making online friends and dynamics of online social networks. Inspired by recent causal process based recommendations that first model user exposures towards items and then use these exposures to guide rating prediction, we utilize social information to capture user exposures rather than user preferences. We assume that people get information of products from their online friends and they do not have to share similar preferences, which is less restrictive and seems closer to reality. Under this new assumption, in this paper, we present a novel recommendation approach (named SERec) to integrate social exposure into collaborative filtering. We propose two methods to implement SERec, namely social regularization and social boosting, each with different ways to construct social exposures. Experiments on four real-world datasets demonstrate that our methods outperform the state-of-the-art methods on top-N recommendations. Further study compares the robustness and scalability of the two proposed methods.Comment: Accepted for publication at the 32nd Conference on Artificial Intelligence (AAAI 2018), New Orleans, Louisian

Democracy and economic growth: a perspective of cooperation

Does democracy cause higher economic growth? We build a model taking culture and interpersonal cooperation into account and find that democracy increases economic productivity through giving people more equal rights, which allows people to build a larger interpersonal network so that they can reduce investment risk and employ high-productivity (high-risk) methods in production

Finite-temperature critical behaviors in 2D long-range quantum Heisenberg model

The well-known Mermin-Wagner theorem prohibits the existence of finite-temperature spontaneous continuous symmetry breaking phase in systems with short-range interactions at spatial dimension $D\le 2$ [Phys. Rev. 158, 383; Phys. Rev. Lett. 17, 1133; Journal of Statistical Physics 175, 521-529]. For long-range interaction with monotonic power-law form ($1/r^{\alpha}$), the theorem further forbids a ferro- or antiferromagnetic order at finite temperature when $\alpha\ge 2D$[Phys. Rev. Lett. 87, 137203]. However, the situation for $\alpha \in (2,4)$ at $D=2$ is beyond the predicting power of the theorem and the situation is still unclear. Here we address this question by large-scale quantum Monte Carlo simulations, accompanied with field theoretical analysis. We find the spontaneous breaking of the $SU(2)$ symmetry for $\alpha \in (2,4)$ in ferromagnetic Heisenberg model with $1/r^{\alpha}$ interaction at $D=2$, and obtain the accurate critical exponents by finite-size analysis for $\alpha<3$ where the system is above the upper critical dimension with Gaussian fixed point and for $3\le\alpha<4$ where the system is below the upper critical dimension with non-Gaussian fixed point. Our results reveal the novel critical behaviors in 2D long-range Heisenberg models and will intrigue further experimental studies of quantum materials with long-range interaction beyond the realm of the Mermin-Wagner theorem

Quantum criticality and entanglement for 2d long-range Heisenberg bilayer

The study of quantum criticality and entanglement in systems with long-range (LR) interactions is still in its early stages, with many open questions remaining. In this work, we investigate critical exponents and scaling of entanglement entropies (EE) in the LR bilayer Heisenberg model using large-scale quantum Monte Carlo (QMC) simulations and the recently developed nonequilibrium increment algorithm for measuring EE. By applying modified (standard) finite-size scaling (FSS) above (below) the upper critical dimension and field theory analysis, we obtain precise critical exponents in three regimes: the LR Gaussian regime with a Gaussian fixed point, the short-range (SR) regime with Wilson-Fisher (WF) exponents, and a LR non-Gaussian regime where the critical exponents vary continuously from LR Gaussian to SR values. We compute the R\'enyi EE both along the critical line and in the N\'eel phase and observe that as the LR interaction is enhanced, the area-law contribution in EE gradually vanishes both at quantum critical points (QCPs) and in the N\'eel phase. The log-correction in EE arising from sharp corners at the QCPs also decays to zero as LR interaction grows, whereas the log-correction for N\'eel states, caused by the interplay of Goldstone modes and restoration of the symmetry in a finite system, is enhanced as LR interaction becomes stronger. We also discuss relevant experimental settings to detect these nontrivial properties in critical behavior and entanglement information for quantum many-body systems with LR interactions.Comment: 5pages, 4 figure

Resummation-based Quantum Monte Carlo for Entanglement Entropy Computation

Based on the recently developed resummation-based quantum Monte Carlo method for the SU($N$) spin and loop-gas models, we develop a new algorithm, dubbed ResumEE, to compute the entanglement entropy (EE) with greatly enhanced efficiency. Our ResumEE converts the evaluation of the exponentially small value of the $\langle e^{-S^{(2)}}\rangle$, where $S^{(2)}$ is the 2nd order R\'enyi EE, to an important sampling process with polynomial accuracy such that the $S^{(2)}$ for a generic 2D quantum SU($N$) spin models can be readily computed without facing the exponential explosion of its variance. We benchmark our algorithm with the previously proposed estimators of $S^{(2)}$ on 1D and 2D SU($2$) Heisenberg spin systems to reveal its superior performance and then use it to detect the entanglement scaling data of the N\'eel-to-VBS transition on 2D SU($N$) Heisenberg model with continuously varying $N$. Our ResumEE algorithm solves the critical problem of precisely evaluating the quantum entanglement in many-body systems and will have a significant impact on reliable access to the conformal field theory data for the highly entangled quantum matter.Comment: 10 pages, 7 figure

Dynamical properties of quantum many-body systems with long range interactions

Employing large-scale quantum Monte Carlo simulations, we systematically compute the energy spectra of the 2D spin-1/2 Heisenberg model with long-range interactions. With the $1/r^{\alpha}$ ferromagnetic and staggered antiferromagnetic interactions, we find the explicit range in $\alpha$ for {\color{black} the short-range Goldstone-type (gapless), anomalous Goldstone-type (gapless) and Higgs-type (gapped) spectra. Accompanied by the spin wave analysis, our numerical results vividly reveal how the long-range interactions alter the usual linear and quadratic magnon dispersions in 2D quantum magnets and give rise to anomalous dynamical exponents. Moreover, we find explicit case where the gapped excitation exists even when the Hamiltonian is extensive. This work provides the first set of unbiased dynamical data} of long-range quantum many-body systems and suggests that many universally accepted low-energy customs for short-range systems need to be substantially modified for long-range ones which are of immediate relevance to the ongoing experimental efforts from quantum simulators to 2D quantum moir\'e materials.Comment: 5 pages,3 figure

Member stability of stainless steel welded I-section beam-columns

A comprehensive experimental and numerical study is presented into the behaviour of stainless steel welded I-section beams-columns. Twenty test specimens were fabricated from grade 304 (EN 1.4301) austenitic and grade 2205 (EN 1.4406) duplex stainless steel plates – ten were tested under major axis bending plus compression and ten under minor axis bending plus compression. Material tensile coupon tests and geometric imperfection measurements were also conducted. Numerical models were developed, calibrated against the test results and subsequently employed in parametric studies considering a wider range of specimen geometries. Based on the obtained test and numerical results, the accuracy and reliability of existing design rules given in EN 1993-1-4 and AISC DG 27, as well as recent proposals, were assessed

Member stability of stainless steel welded I-section beam-columns

A comprehensive experimental and numerical study is presented into the behaviour of stainless steel welded I-section beams-columns. Twenty test specimens were fabricated from grade 304 (EN 1.4301) austenitic and grade 2205 (EN 1.4406) duplex stainless steel plates – ten were tested under major axis bending plus compression and ten under minor axis bending plus compression. Material tensile coupon tests and geometric imperfection measurements were also conducted. Numerical models were developed, calibrated against the test results and subsequently employed in parametric studies considering a wider range of specimen geometries. Based on the obtained test and numerical results, the accuracy and reliability of existing design rules given in EN 1993-1-4 and AISC DG 27, as well as recent proposals, were assessed