Unified Loss of Pair Similarity Optimization for Vision-Language Retrieval

There are two popular loss functions used for vision-language retrieval, i.e., triplet loss and contrastive learning loss, both of them essentially minimize the difference between the similarities of negative pairs and positive pairs. More specifically, Triplet loss with Hard Negative mining (Triplet-HN), which is widely used in existing retrieval models to improve the discriminative ability, is easy to fall into local minima in training. On the other hand, Vision-Language Contrastive learning loss (VLC), which is widely used in the vision-language pre-training, has been shown to achieve significant performance gains on vision-language retrieval, but the performance of fine-tuning with VLC on small datasets is not satisfactory. This paper proposes a unified loss of pair similarity optimization for vision-language retrieval, providing a powerful tool for understanding existing loss functions. Our unified loss includes the hard sample mining strategy of VLC and introduces the margin used by the triplet loss for better similarity separation. It is shown that both Triplet-HN and VLC are special forms of our unified loss. Compared with the Triplet-HN, our unified loss has a fast convergence speed. Compared with the VLC, our unified loss is more discriminative and can provide better generalization in downstream fine-tuning tasks. Experiments on image-text and video-text retrieval benchmarks show that our unified loss can significantly improve the performance of the state-of-the-art retrieval models.Comment: 16 pages, 5 figure

Promotion of Au nanoparticles on carbon frameworks for alkali-free aerobic oxidation of benzyl alcohol

We synthesized a series of modified Co-ZIF-67 materials with tunable morphology to support fine Au nanoparticles for the alkali-free aerobic oxidation of benzyl alcohol. Structure promotion was performed using Stöber silica as a hard template, which was subsequently removed by NaOH etching before gold immobilization. The texture structure of Au/(Si)C was greatly improved with increasing surface area and volume. CoOx was simultaneously introduced into the carbon shell from the Co-ZIF-67 precursor, which consequently facilitated the specific Au-support interaction via bimetallic synergy. XRD, XPS, and TEM images demonstrated the redispersion of both Au and CoOx as well as the electronic delivery between metals. Analysis of the chemical and surface composition suggested a surface rich in Auδ+ with abundant lattice oxygen contributed by CoOx in the final Au/(Si)C, which improved the transformation rate of benzyl alcohol even in an alkali-free condition. Au/(Si)C with finely dispersed Au particles showed excellent catalytic performance in the alkali-free environment, with 89.3% benzyl conversion and 74.5% benzaldehyde yield under very mild conditions

Catalytic oxidative C-C bond cleavage route of levulinic acid and methyl levulinate

Recently, obtaining value-added chemicals from biomass resources has attracted considerable attention. Levulinic acid is one of the most important biomass platform compounds, which could be obtained from carbohydrate biomass. In this work, levulinic acid was selectively converted into C4 product, including succinic anhydride, via catalytic oxidation with a manganese catalyst in acetic anhydride. Moreover, an unexpected product of maleic anhydride was obtained, which greatly differs from that of levulinate ester. The pathway for formation of maleic anhydride was studied by monitoring and confirming intermediates alpha-angelica lactone and its derivative 2-methyl-5-oxotetrahydro-2-furanyl acetate. Based on the obtained mechanistic information, the different behaviour between the oxidative cleavage of levulinic acid and levulinate ester was further discussed

Novel Effect of Zinc Nitrate/Vanadyl Oxalate for Selective Catalytic Oxidation of α-Hydroxy Esters to α-Keto Esters with Molecular Oxygen: An In Situ ATR-IR Study

Selective oxidation of α-hydroxy esters is one of the most important methods to prepare high value-added α-keto esters. An efficient catalytic system consisting of Zn(NO3)2/VOC2O4 is reported for catalytic oxidation of α-hydroxy esters with molecular oxygen. Up to 99% conversion of methyl DL-mandelate or methyl lactate could be facilely obtained with high selectivity for its corresponding α-keto ester under mild reaction conditions. Zn(NO3)2 exhibited higher catalytic activity in combination with VOC2O4 compared with Fe(NO3)3 and different nitric oxidative gases were detected by situ attenuated total reflection infrared (ATR-IR) spectroscopy. UV-vis and ATR-IR results indicated that coordination complex formed in Zn(NO3)2 in CH3CN solution was quite different from Fe(NO3)3; it is proposed that the charge-transfer from Zn2+ to coordinated nitrate groups might account for the generation of different nitric oxidative gases. The XPS result indicate that nitric oxidative gas derived from the interaction of Zn(NO3)2 with VOC2O4 could be in favor of oxidizing VOC2O4 to generate active vanadium (V) species. It might account for different catalytic activity of Zn(NO3)2 or Fe(NO3)3 combined with VOC2O4. This work contributes to further development of efficient aerobic oxidation under mild reaction conditions

studiesontherolesofvanadylsulfateandsodiumnitriteincatalyticoxidationofbenzylalcoholwithmolecularoxygen

An efficient catalytic system consisting of vanadyl sulfate/sodium nitrite was disclosed previously for the oxidation of benzylic alcohols into aldehydes with molecular oxygen. However, the roles of catalyst components were not investigated. In this paper, we examined catalytic oxidation of benzyl alcohol as a model reaction, especially by infrared spectroscopy. The role of each component is discussed including nitrite, vanadyl, sulphate, and water. Sodium nitrite could be converted into nitrate and nitric acid. The vanadium(IV) could be smoothly oxidized into vanadium(V) under mild and acidic conditions without any organic ligands. The transformation of sulfate and bisulfate, the cessation of an induction period, and the oxidation of benzyl alcohol were closely interrelated. The multiple roles of water are discussed, including reduction of the induction period, participation in redox cycles of nitric compounds, deactivation of vanadium, and as a byproduct of oxidation. This study contributes to further development of aerobic oxidation using vanadium based catalysts

Aqueous phase hydrogenation of furfural to tetrahydrofurfuryl alcohol on alkaline earth metal modified Ni/Al2O3

Al2O3 modified by alkaline earth metals M-Al2O3 (M - Mg, Ca, Sr, Ba) was synthesised by coprecipitation method. The nickel-based catalysts supported by M-Al2O3 were prepared by impregnation method. The catalysts were characterized by TEM, N-2 adsorption/desorption, XRD, H-2-TPR, NH3-TPD and XPS, and used for the direct hydrogenation of furfural to tetrahydrofurfuryl alcohol (THFA) in water. The reaction was demonstrated to proceed through furfuryl alcohol as an intermediate. The modification of Al2O3 by alkaline earth metals has a significant effect on the activity and selectivity of THFA. A high yield of THFA was obtained over Ni/Ba-Al2O3 under optimized conditions. Moreover, the catalyst is recyclable and reusable at least four times without significant loss of the conversion of furfural and selectivity of THFA

Mechanistic studies on the VO(acac)(2)-catalyzed oxidative cleavage of lignin model compounds in acetic acid

Lignin is the primary source of aromatic chemicals in nature. Selective aerobic oxidation has provided a promising approach for breaking lignin into smaller aromatics. During VO(acac)(2)-catalyzed oxidation of lignin model compound 2-phenoxy-1-phenylethanol, benzaldehyde was unexpectedly observed as a product, in contrast to the results reported previously. The reaction pathway was studied, and a hemiacetal-like intermediate was found to be involved, and the similar intermediate was also observed during oxidation of model compound benzyl phenyl ether. Compared with direct C-O bond cleavage, prior formation of hemiacetal-like structures via oxidation would be expected to facilitate the cleavage of the aryl ether bond in aralkyl aryl ethers under mild reaction conditions

studiesontherolesofvanadylsulfateandsodiumnitriteincatalyticoxidationofbenzylalcoholwithmolecularoxygen

An efficient catalytic system consisting of vanadyl sulfate/sodium nitrite was disclosed previously for the oxidation of benzylic alcohols into aldehydes with molecular oxygen. However, the roles of catalyst components were not investigated. In this paper, we examined catalytic oxidation of benzyl alcohol as a model reaction, especially by infrared spectroscopy. The role of each component is discussed including nitrite, vanadyl, sulphate, and water. Sodium nitrite could be converted into nitrate and nitric acid. The vanadium(IV) could be smoothly oxidized into vanadium(V) under mild and acidic conditions without any organic ligands. The transformation of sulfate and bisulfate, the cessation of an induction period, and the oxidation of benzyl alcohol were closely interrelated. The multiple roles of water are discussed, including reduction of the induction period, participation in redox cycles of nitric compounds, deactivation of vanadium, and as a byproduct of oxidation. This study contributes to further development of aerobic oxidation using vanadium based catalysts

Dehydrogenation of primary aliphatic alcohols to aldehydes over Cu-Ni bimetallic catalysts

The catalytic conversion of non-activated primary aliphatic alcohols to aldehydes is a challenge, and monometallic Cu-based catalysts loaded on different supports have often been used for these reactions. Cu-Ni/gamma-Al2O3 bimetallic catalysts were prepared and used for anaerobic dehydrogenation of 3,3-dimethyl-1-butanol to 3,3-dimethyl-1-butanal. These catalysts exhibited higher activity than Cu/gamma-Al2O3 under the same reaction conditions, and a wide range of primary aliphatic alcohols were efficiently converted to the corresponding aldehydes over Cu-Ni/gamma-Al2O3 under mild conditions. (C) 2014, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved