Exploring the Spatiotemporal Features of Online Food Recommendation Service

Online Food Recommendation Service (OFRS) has remarkable spatiotemporal characteristics and the advantage of being able to conveniently satisfy users' needs in a timely manner. There have been a variety of studies that have begun to explore its spatiotemporal properties, but a comprehensive and in-depth analysis of the OFRS spatiotemporal features is yet to be conducted. Therefore, this paper studies the OFRS based on three questions: how spatiotemporal features play a role; why self-attention cannot be used to model the spatiotemporal sequences of OFRS; and how to combine spatiotemporal features to improve the efficiency of OFRS. Firstly, through experimental analysis, we systemically extracted the spatiotemporal features of OFRS, identified the most valuable features and designed an effective combination method. Secondly, we conducted a detailed analysis of the spatiotemporal sequences, which revealed the shortcomings of self-attention in OFRS, and proposed a more optimized spatiotemporal sequence method for replacing self-attention. In addition, we also designed a Dynamic Context Adaptation Model to further improve the efficiency and performance of OFRS. Through the offline experiments on two large datasets and online experiments for a week, the feasibility and superiority of our model were proven.Comment: accepted by SIGIR 202

Multi-Granularity Attention Model for Group Recommendation

Group recommendation provides personalized recommendations to a group of users based on their shared interests, preferences, and characteristics. Current studies have explored different methods for integrating individual preferences and making collective decisions that benefit the group as a whole. However, most of them heavily rely on users with rich behavior and ignore latent preferences of users with relatively sparse behavior, leading to insufficient learning of individual interests. To address this challenge, we present the Multi-Granularity Attention Model (MGAM), a novel approach that utilizes multiple levels of granularity (i.e., subsets, groups, and supersets) to uncover group members' latent preferences and mitigate recommendation noise. Specially, we propose a Subset Preference Extraction module that enhances the representation of users' latent subset-level preferences by incorporating their previous interactions with items and utilizing a hierarchical mechanism. Additionally, our method introduces a Group Preference Extraction module and a Superset Preference Extraction module, which explore users' latent preferences on two levels: the group-level, which maintains users' original preferences, and the superset-level, which includes group-group exterior information. By incorporating the subset-level embedding, group-level embedding, and superset-level embedding, our proposed method effectively reduces group recommendation noise across multiple granularities and comprehensively learns individual interests. Extensive offline and online experiments have demonstrated the superiority of our method in terms of performance

Direct synthesis and characterization of pore-broadened Al-SBA-15

A series of pore-broadened Al-SBA-15 samples were synthesized using a direct hydrothermal method. The effects of aluminum incorporation, assembling temperature, and co-solvent (1,3,5-trimethylbenzene (TMB)) content were investigated by low-angle XRD, N-2 adsorption and desorption isotherm analysis, SEM, TEM, NH3-TPD, FTIR, pyridine-IR, and Al-27 NMR. The results indicated that aluminum incorporation (Si/Al ratio = 10) increased the pore size of SBA-15 from 5.66 to 10.13 nm. A small pore size of 6.55 nm was observed at a low assembling temperature of 30 degrees C, attributing to the inadequate stretching of the molecular template. An increased pore size of 8.45 nm was obtained at an assembling temperature of 60 degrees C because of the partial hydrophobization of the hydrophilic groups, whereas a high temperature of 70 degrees C resulted in the generation of least ordered pores. The hydrophobic co-solvent TMB showed a significant broadening level as a result of its effective fusion into the hydrophobic micelle cores. A highly ordered pore framework with a pore size of 18 nm was obtained at a TMB/P-123 ratio of 0.25, which was found to be optimum. More or less TMB led to the generation of mesocellular silica-aluminum foams with a complete loss of regularity. The Al-27 NMR results showed that aluminum was mostly tetrahedrally coordinated. The NH3-TPD and pyridine-IR detection results indicated that a number of weak and medium acid sites (as Bronsted and Lewis acid sites) existed in Al-SBA-15 pore-broadened by TMB. (C) 2016 Elsevier Inc. All rights reserved

Highly stable gasified straw slag as a novel solid base catalyst for the effective synthesis of biodiesel: Characteristics and performance

A novel solid base catalyst derived from gasified straw slag for producing biodiesel was prepared by simple pulverization and sieving. This catalyst exhibited high stability, low leaching of the catalytic species, and good catalytic activity, caused by high -temperature melting in the biomass gasifier. SiO2, CaO, K2O, MgO, FeO, and A1(2)O(3) were the common constituents (calculated as oxides) as per XRF analysis and EA. XRD and TEM-EDS analysis indicated that the catalyst comprises three crystallites: quartz, leucite, and dkermanite. The catalyst was strongly basic with a basic site concentration of 0.3974 mniol.g(-1), including strongly basic low-coordination oxygen anions, moderately basic OH groups, and metal-oxygen pairs, as identified by CO2-TPD and IR. TGA results indicated that the catalyst is thermally stable up to 400 degrees C, which is greater than the typical reaction temperature. BET analysis results indicated that the slag exhibits a broad pore distribution with pore diameters of 5-15 and 45-75 nm. The catalyst exhibited high catalytic activity and stability, exhibiting a fatty acid methyl ester (FAME) conversion of 95% for transesterification conducted at 200 degrees C for 8 h with a catalyst dose of 20% and a methanol-oil molar ratio of 12:1. The FAME conversion remained greater than 85% even after reusing the catalyst for 33 reactions without any appreciable loss of catalytic activity. Small amounts of K and Mg (<10 ppm) leached into the product from the catalyst. These results indicated that the gasified straw slag catalyst demonstrates promise for producing biodiesel. (C) 2017 Elsevier Ltd. All rights reserved

Synthesis of Glycerol-Free Biodiesel with Dimethyl Carbonate over Sulfonated Imidazolium Ionic Liquid

Ionic liquid is a green solvent and catalyst. A new approach of using dimethyl carbonate (DMC) catalyzed by sulfonated imidazolium ionic liquid (SIIL) producing glycerol-free biodiesel was developed. Together with the fatty acid methyl ester (FAME), the other two products fatty acid 1,3-dimethoxypropyl ester and 1,3-dimethoxypropan-2-ol were also generated, which could be used as an oxygenate additive without separation from biodiesel. The overall reaction pathway was resolved upon the product analysis, which could well explain the whole process and product distributions. In this paper, the effects of the molar ratio of DMC/rapeseed oil, catalyst dosage, reaction temperature, and reaction time were explored. The highest yield of FAME with the SIIL catalyst 1-propylsulfonate-3-methylimidazolium hydrogen sulfate ([PrSO3HMIM][HSO4]) reached 95.77% under optimum conditions

Sulfonated imidazolium ionic liquid-catalyzed transesterification for biodiesel synthesis

Four kinds of imidazolium ionic liquids (ILs) were employed to catalyze the transesterification reaction of rapeseed oil. The effects of molar ratio of methanol to rapeseed oil, catalyst dosage, reaction temperature, and reaction time, and the deactivation of water on catalytic activity were explored. The results showed that imidazolium ILs with long alkyl chains and sulfonated groups exhibited the best catalytic activities due to their strong Bronsted acidity. The catalytic activity was depend on the -SO3H group in the cation, not the anion HSO4. Water molecules competed with the anion to bind with the protons of the imidazolium cation. This results in the disruption of the structure of ILs, leading to deactivation; increasing the reaction temperature could alleviate this negative effect of water. The yield of fatty acid methyl ester (FAME) remained constant (similar to 85%) at 130 degrees C, when the water content increased from 1 wt% to 5 wt%. The highest yield of FAME for the catalyst 1-butylsulfonate-3-methyl imidazolium hydrogen sulfate ([BSO3HMIM][HSO4]) could reach 100% under optimum conditions. (C) 2016 Elsevier Ltd. All rights reserved

Sulfonated imidazolium ionic liquid-catalyzed transesterification for biodiesel synthesis

Four kinds of imidazolium ionic liquids (ILs) were employed to catalyze the transesterification reaction of rapeseed oil. The effects of molar ratio of methanol to rapeseed oil, catalyst dosage, reaction temperature, and reaction time, and the deactivation of water on catalytic activity were explored. The results showed that imidazolium ILs with long alkyl chains and sulfonated groups exhibited the best catalytic activities due to their strong Bronsted acidity. The catalytic activity was depend on the -SO3H group in the cation, not the anion HSO4. Water molecules competed with the anion to bind with the protons of the imidazolium cation. This results in the disruption of the structure of ILs, leading to deactivation; increasing the reaction temperature could alleviate this negative effect of water. The yield of fatty acid methyl ester (FAME) remained constant (similar to 85%) at 130 degrees C, when the water content increased from 1 wt% to 5 wt%. The highest yield of FAME for the catalyst 1-butylsulfonate-3-methyl imidazolium hydrogen sulfate ([BSO3HMIM][HSO4]) could reach 100% under optimum conditions. (C) 2016 Elsevier Ltd. All rights reserved

One-step hydroprocessing of fatty acids into renewable aromatic hydrocarbons over Ni/HZSM-5: insights into the major reaction pathways

For high caloricity and stability in bio-aviation fuels, a certain content of aromatic hydrocarbons (AHCs, 8-25 wt%) is crucial. Fatty acids, obtained from waste or inedible oils, are a renewable and economic feedstock for AHC production. Considerable amounts of AHCs, up to 64.61 wt%, were produced through the one-step hydroprocessing of fatty acids over Ni/HZSM-5 catalysts. Hydrogenation, hydrocracking, and aromatization constituted the principal AHC formation processes. At a lower temperature, fatty acids were first hydrosaturated and then hydrodeoxygenated at metal sites to form long-chain hydrocarbons. Alternatively, the unsaturated fatty acids could be directly deoxygenated at acid sites without first being saturated. The long-chain hydrocarbons were cracked into gases such as ethane, propane, and C-6-C-8 olefins over the catalysts' Bronsted acid sites; these underwent Diels-Alder reactions on the catalysts' Lewis acid sites to form AHCs. C-6-C-8 olefins were determined as critical intermediates for AHC formation. As the Ni content in the catalyst increased, the Bronsted-acid site density was reduced due to coverage by the metal nanoparticles. Good performance was achieved with a loading of 10 wt% Ni, where the Ni nanoparticles exhibited a polyhedral morphology which exposed more active sites for aromatization