Task Relation-aware Continual User Representation Learning

User modeling, which learns to represent users into a low-dimensional representation space based on their past behaviors, got a surge of interest from the industry for providing personalized services to users. Previous efforts in user modeling mainly focus on learning a task-specific user representation that is designed for a single task. However, since learning task-specific user representations for every task is infeasible, recent studies introduce the concept of universal user representation, which is a more generalized representation of a user that is relevant to a variety of tasks. Despite their effectiveness, existing approaches for learning universal user representations are impractical in real-world applications due to the data requirement, catastrophic forgetting and the limited learning capability for continually added tasks. In this paper, we propose a novel continual user representation learning method, called TERACON, whose learning capability is not limited as the number of learned tasks increases while capturing the relationship between the tasks. The main idea is to introduce an embedding for each task, i.e., task embedding, which is utilized to generate task-specific soft masks that not only allow the entire model parameters to be updated until the end of training sequence, but also facilitate the relationship between the tasks to be captured. Moreover, we introduce a novel knowledge retention module with pseudo-labeling strategy that successfully alleviates the long-standing problem of continual learning, i.e., catastrophic forgetting. Extensive experiments on public and proprietary real-world datasets demonstrate the superiority and practicality of TERACON. Our code is available at https://github.com/Sein-Kim/TERACON.Comment: KDD 202

Structures, phase transitions, and nonlinear optical properties of ultra-thin molecular films

Ultra-thin molecular films with a thickness below a few hundred nanometers are currently of special interest in surface and material science/technology. Although many studies have concentrated on adsorbate-substrate and inter-molecular interactions, it still remain to be explored how adsorbate-substrate and inter-molecular interactions affect the growth and structure of ultra-thin molecular film. In this thesis, second harmonic generation (SHG), a nonlinear optical phenomenon, has been utilized, in combination with traditional surface techniques such as TPD and EELS, to investigate structure, growth mechanisms, and phase transitions in ultra-thin molecular films. The ultra-thin molecular films of our interest consist of small/moderate polyatomic molecules, such as benzene, pyridine, aniline, and water. Crystallization kinetics and premelting in pyridine films (within 100 nm thickness) have been characterized. Non-equilibrium nucleation, followed by pre-melting, was first observed for thin films of aniline. Various types of layer-by-layer structures for benzene, pyridine, and aniline (within 5 nm thickness) were observed, and the influence of both molecular geometry and interactions on nanostructures is discussed. Second harmonic Rayleigh scattering was introduced to monitor the glass transition of supercooled water produced in the form of a molecular thin film. This is the first reported optical detection of the glass transition for supercooled water. In addition, SHG was successfully used for the first time, to investigate nucleation and wetting/dewetting processes for a weakly binding system such as water molecules on silver surfaces. Finally, the temperature dependence and effect of adsorption on SHG resonantly enhanced by a surface-state transition of the Ag(110) surface was investigated

Structures, phase transitions, and nonlinear optical properties of ultra-thin molecular films

Ultra-thin molecular films with a thickness below a few hundred nanometers are currently of special interest in surface and material science/technology. Although many studies have concentrated on adsorbate-substrate and inter-molecular interactions, it still remain to be explored how adsorbate-substrate and inter-molecular interactions affect the growth and structure of ultra-thin molecular film. In this thesis, second harmonic generation (SHG), a nonlinear optical phenomenon, has been utilized, in combination with traditional surface techniques such as TPD and EELS, to investigate structure, growth mechanisms, and phase transitions in ultra-thin molecular films. The ultra-thin molecular films of our interest consist of small/moderate polyatomic molecules, such as benzene, pyridine, aniline, and water. Crystallization kinetics and premelting in pyridine films (within 100 nm thickness) have been characterized. Non-equilibrium nucleation, followed by pre-melting, was first observed for thin films of aniline. Various types of layer-by-layer structures for benzene, pyridine, and aniline (within 5 nm thickness) were observed, and the influence of both molecular geometry and interactions on nanostructures is discussed. Second harmonic Rayleigh scattering was introduced to monitor the glass transition of supercooled water produced in the form of a molecular thin film. This is the first reported optical detection of the glass transition for supercooled water. In addition, SHG was successfully used for the first time, to investigate nucleation and wetting/dewetting processes for a weakly binding system such as water molecules on silver surfaces. Finally, the temperature dependence and effect of adsorption on SHG resonantly enhanced by a surface-state transition of the Ag(110) surface was investigated

Fully private and secure coded matrix multiplication with colluding workers

In this paper, we propose a new coded computation scheme that can alleviate straggler effects in distributed computing. We consider data security and master’s privacy for matrix multiplication tasks. The proposed scheme, called fully private and secure coded matrix multiplication (FPSCMM), ensures data security and master’s privacy on two data matrices for multiplication tasks from colluding workers. We also show that the storage overhead at workers can be reduced by FPSCMM, since it is enough for workers to store the encoded matrices with sub-blocks. Lastly, we compare FPSCMM with the existing master’s privacy-preserving coded matrix multiplication schemes

Repair Rates for Multiple Descriptions on Distributed Storage

In a traditional distributed storage system, a source can be restored perfectly when a certain subset of servers is contacted. The coding is independent of the contents of the source. This paper considers instead a lossy source coding version of this problem where the more servers that are contacted, the higher the quality of the restored source. An example could be video stored on distributed storage. In information theory, this is called the multiple description problem, where the distortion depends on the number of descriptions received. The problem considered in this paper is how to restore the system operation when one of the servers fail and a new server replaces it, that is, repair. The requirement is that the distortions in the restored system should be no more than in the original system. The question is how many extra bits are needed for repair. We find an achievable rate and show that this is optimal in certain cases. One conclusion is that it is necessary to design the multiple description codes with repair in mind; just using an existing multiple description code results in unnecessary high repair rates