High Conversion Rate Research Articles

New Cu(II) Schiff-base complex modified on magnetic nanoparticles: Oxidation and DFT investigation

A copper magnetic nanocatalyst was facilely synthesized by surface modification of silica magnetic nanoparticles (Fe3O4@SiO2) via reaction with 3-aminopropyltrimethoxysilane (Fe3O4@SiO2@APTMS), followed by a subsequent reaction with thiophene-2-carbaldehyde to form a Schiff base (Fe3O4@SiO2@SB). Sequentially, reaction with Cu(CH3COO)2·H2O in ethanol yielded Fe3O4@SiO2@[SB@Cu] (CH3COO)2. This nanomagnetic catalyst was comprehensively characterized using Fourier Transform Infrared Spectroscopy (FT-IR), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Thermogravimetric Analysis (TGA), and Vibrating Sample Magnetometry (VSM) techniques. The catalytic proficiency of these nanoparticles was evaluated through alkene and alcohol oxidation reactions. Under optimized conditions, the nanocatalyst exhibited significant efficacy in oxidizing styrene, cyclohexene, and benzyl alcohol, with notable selectivity values of 88 %, 100 %, and 100 % for the respective formation of styrene epoxide, 2-cyclohexene-1-one, and benzoic acid. The heterogeneous copper nanocatalyst offers advantages, including high conversion rates, facile separation, and exceptional selectivity in alkene and alcohol oxidation. Additionally, this study investigated density functional theory (DFT) methods, encompassing geometric optimization, natural charge analysis, molecular electrostatic potential maps, and vibrational normal modes of the chelating ligands.

Hierarchical porous Pd/HS-1 zeolite as an efficient and reusable catalysts for Suzuki-Miyaura reaction

The Suzuki-Miyaura reaction is one of the most effective routes for the construction of carbon–carbon bonds, due to the obvious advantages of mild reaction conditions, wide range of functional group tolerance, simplicity of operation, and environmental friendliness. However, these reactions highly depend on the development of the active and stable catalysts. Herein, the hollow hexagonal prismatic silicalite-1 (HS-1) zeolite-supported palladium nanoparticles (Pd NPs) were synthesized and applied as a catalyst in Suzuki-Miyaura reaction. The experimental results show that 2.0Pd/HS-1 is an efficient and stable catalyst, which can achieve a high conversion rate (>99.9 %) in a short time (45 min) and can be recycled. Further studies show that 2.0Pd/HS-1 has abundant mesopores, which are favorable for exposing more active sites and promoting the transfer of reactants around the catalysts, thus improving the contact opportunities between the catalysts and the feedstock. Moreover, its proper acid sites as well as metal-zeolite interactions can modulate the electronic state of Pd, and thus improve the conversion of bromobenzene. This work provides new insights into the design, synthesis and applications of highly efficient hollow silicalite-1 zeolite loaded metal catalysts.

Structured nanoporous Cu/ZnO catalysts for on-board methanol steam reforming prepared by laser powder bed fusion and dealloying

The development of efficient structural catalysts and reactors (SCRs) for on-board methanol steam reforming (MSR) has long been a focal point. Traditional MSR SCRs exhibit problems such as poor heat transfer, low catalyst loading, and coating delamination. In this study, novel three-dimensional graded nanoporous Cu/ZnO (3DNP-Cu/ZnO) SCRs were prepared via metal 3D printing technology and dealloying. For 3DNP-Cu/ZnO SCRs activated with MeOH/H2O steam, both the interfacial area of Cu-ZnO and the Cu+/(Cu0 + Cu+) molar ratio were greater than those of catalysts activated with H2/N2 mixtures. The experimental results showed that a 3DNP-Cu/ZnO SCR activated with MeOH/H2O for 20 min exhibited a high methanol conversion rate of 98.3 % with a CO selectivity of 0.86 % (with a reaction temperature of 280 °C, a water-to-alcohol molar ratio of 1.3 and a weight hourly space velocity of 30 h−1). The superior catalytic activity was attributed to the high Cu+/(Cu++Cu0) ratio, which enabled the generation of *CHOO during the MSR reaction. Additionally, the 3DNP-Cu/ZnO SCRs demonstrated low pressure drops and high mechanical strengths. Computational fluid dynamics simulations showed that the gyroid lattice-structured catalyst achieved a high H2 concentration due to its high mass and heat transfer. 3DNP-Cu/ZnO SCRs provide a new strategy for the preparation of MSR SCRs with broad application prospects.

Biotransformation of HBCDs by the microbial communities enriched from mangrove sediments

1,2,5,6,9,10-Hexabromocyclododecanes (HBCDs) are a sort of persistent organic pollutants (POPs). This research investigated 12 microbial communities enriched from sediments of four mangroves in China to transform HBCDs. Six microbial communities gained high transformation rates (27.5–97.7%) after 12 generations of serial transfer. Bacteria were the main contributors to transform HBCDs rather than fungi. Analyses on the bacterial compositions and binning genomes showed that Alcanivorax (55.246–84.942%) harboring haloalkane dehalogenase genes dadAH and dadBH dominated the microbial communities with high transformation rates. Moreover, expressions of dadAH and dadBH in the microbial communities and Alcanivorax isolate could be induced by HBCDs. Further, it was found that purified proteins DadAH and DadBH showed high conversion rates on HBCDs in 36 h (91.9 ± 7.4 and 101.0 ± 1.8%, respectively). The engineered Escherichia coli BL21 strains harbored two genes could convert 5.7 ± 0.4 and 35.1 ± 0.1% HBCDs, respectively, lower than their cell-free crude extracts (61.2 ± 5.2 and 56.5 ± 8.7%, respectively). The diastereoisomer-specific transforming trend by both microbial communities and enzymes were γ- > α- > β-HBCD, differed from α- > β- > γ-HBCD by the Alcanivorax isolate. The identified transformation products indicated that HBCDs were dehalogenated via HBr elimination (dehydrobromination), hydrolytic and reductive debromination pathways in the enriched cultures. Two enzymes converted HBCDs via hydrolytic debromination. The present research provided theoretical bases for the biotransformation of HBCDs by microbial community and the bioremediation of HBCDs contamination in the environment.

Potential of (La-)NiCu catalysts for the hydrodeoxygenation of 4-(2-furanyl)-3-buten-2-one into fuels: Investigation of support and La addition

Aiming at the valorization of furfural-derived compounds, the potential of (La-)NiCu catalysts for the hydrodeoxygenation of 4-(2-furanyl)-3-buten-2-one has been assessed. The impact of support acidity and the effects of modifying the support with La have been explored. While catalysts with non-acidic supports solely lead to hydrogenation, the acid sites enable furanic ring opening. Additionally, changing the support alters the metal-support interaction strength, with stronger interactions reducing the NiCu alloy particle size and increasing activity. Furthermore, according to Density of States calculations, La further enhances the hydrodeoxygenation activity by increasing the adsorption strength. Also, for the acidic supports, it increases the relative abundance of NiCu alloy on the support surface, further increasing the specific activity. The La-NiCu-Al catalyst demonstrated was the best performing catalyst at 200 °C and 40 bar H2, achieving a high conversion rate of 77 mol kgcat−1 h−1 with a combined selectivity of 29 % towards octane and BTHF at 99 % conversion, and stability over 5 hours Time-On-Stream. Additionally, isopropyl alcohol proved to be an excellent hydrogen donor, as the external H2 pressure does not substantially impact the catalyst activity and selectivity, but H2 itself proved to be important for the catalyst stability.

A stable porphyrin-based porous organic polymer as highly efficient heterogeneous photocatalyst for the oxidative homocoupling of amines

With permanent photosensitivity and intrinsic porosity, porphyrin-based porous organic polymers (POPs) are potential candidates for photocatalytic reactions. Herein, H2Pp-POP was prepared via the free radical self-polymerization of [5,10,15,20-tetrakis(4-((4-vinylbenzyl)oxy)phenyl)porphyrin] (H2Pp) containing terminal styrene groups. The as-prepared H2Pp-POP possess superior photosensitivity, abundant pore structure, and robust stability, which endow it remarkable photocatalytic activity and recyclability. As a result, H2Pp-POP exhibits an excellent photocatalytic performance in the oxidative homocoupling of amines into imines, with high conversion rate and selectivity. This study provides a valuable way to synthesize efficient heterogeneous photocatalysts for the conversion of amine.

Advancements of MOFs in the Field of Propane Oxidative Dehydrogenation for Propylene Production.

Compared to the currently widely used propane dehydrogenation process for propylene production, propane oxidative dehydrogenation (ODHP) offers the advantage of no thermodynamic limitations and lower energy consumption. However, a major challenge in ODHP is the occurrence of undesired over-oxidation reactions of propylene, which reduce selectivity and hinder industrialization. MOFs possess a large number of metal sites that can serve as catalytic centers, which facilitates the easier access of reactants to the catalytic centers for reaction. Additionally, their flexible framework structure allows for easier adjustment of their pores compared to metal oxides and molecular sieves, which is advantageous for the diffusion of products within the framework. This property reduces the likelihood of prolonged contact between the generated propylene and the catalytic centers, thus minimizing the possibility of over-oxidation. The research on MOF catalyzed oxidative dehydrogenation of propane (ODHP) mainly focuses on the catalytic properties of MOFs with cobalt oxygen sites and boron oxygen sites. The advantages of cobalt oxygen site MOFs include significantly reduced energy consumption, enabling catalytic reactions at temperatures of 230 °C and below, while boron oxygen site MOFs exhibit high conversion rates and selectivity, albeit requiring higher temperatures. The explicit structure of MOFs facilitates the mechanistic study of these sites, enabling further optimization of catalysts. This paper provides an overview of the recent progress in utilizing MOFs as catalysts for ODHP and explores how they promote progress in ODHP catalysis. Finally, the challenges and future prospects of MOFs in the field of ODHP reactions are discussed.

Tailoring the Electronic Metal-Support Interactions in Supported Silver Catalysts through Al modification for Efficient Ethylene Epoxidation.

Metal-modified catalysts have attracted extraordinary research attention in heterogeneous catalysis due to their enhanced geometric and electronic structures and outstanding catalytic performances. Silver (Ag) possesses necessary active sites for ethylene epoxidation, but the catalyst activity is usually sacrificed to obtain high selectivity towards ethylene oxide (EO). Herein, we report that using Al can help in tailoring the unoccupied 3d state of Ag on the MnO2 support through strong electronic metal-support interactions (EMSIs), overcoming the activity-selectivity trade-off for ethylene epoxidation and resulting in a very high ethylene conversion rate (~100 %) with 90 % selectivity for EO under mild conditions (170 °C and atmospheric pressure). Structural characterization and theoretical calculations revealed that the EMSIs obtained by the Al modification tailor the unoccupied 3d state of Ag, modulating the adsorption of ethylene (C2H4) and oxygen (O2) and facilitating EO desorption, resulting in high C2H4 conversion. Meanwhile, the increased number of positively charge Ag+ lowers the energy barrier for C2H4(ads) oxidation to produce oxametallacycle (OMC), inducing the unexpectedly high EO selectivity. Such an extraordinary electronic promotion provides new promising pathways for designing advanced metal catalysts with high activity and selectivity in selective oxidation reactions.

Tailoring the Electronic Metal‐Support Interactions in Supported Silver Catalysts through Al modification for Efficient Ethylene Epoxidation

AbstractMetal‐modified catalysts have attracted extraordinary research attention in heterogeneous catalysis due to their enhanced geometric and electronic structures and outstanding catalytic performances. Silver (Ag) possesses necessary active sites for ethylene epoxidation, but the catalyst activity is usually sacrificed to obtain high selectivity towards ethylene oxide (EO). Herein, we report that using Al can help in tailoring the unoccupied 3d state of Ag on the MnO2 support through strong electronic metal‐support interactions (EMSIs), overcoming the activity‐selectivity trade‐off for ethylene epoxidation and resulting in a very high ethylene conversion rate (~100 %) with 90 % selectivity for EO under mild conditions (170 °C and atmospheric pressure). Structural characterization and theoretical calculations revealed that the EMSIs obtained by the Al modification tailor the unoccupied 3d state of Ag, modulating the adsorption of ethylene (C2H4) and oxygen (O2) and facilitating EO desorption, resulting in high C2H4 conversion. Meanwhile, the increased number of positively charge Ag+ lowers the energy barrier for C2H4(ads) oxidation to produce oxametallacycle (OMC), inducing the unexpectedly high EO selectivity. Such an extraordinary electronic promotion provides new promising pathways for designing advanced metal catalysts with high activity and selectivity in selective oxidation reactions.

Catalytic cycloaddition of CO2 to epoxidized methyl oleate over a HBimCl-NbCl5/HCMC: Physicochemical, mass transfer and kinetic investigation

The cycloaddition of CO2 to epoxidized molecules is an ecofriendly strategy for synthesizing aliphatic carbonates. In this study, heterogeneous catalytic synthesis of carbonated methyl oleate was performed. Influences of reaction parameters such as reaction temperature (403.15–443.15 K), pressure (1–3 MPa), concentration of functional groups (1.22–2.88 mol·L−1) and catalyst loading (0.025–0.042 g·mL−1) on the kinetics were evaluated. Gas-liquid mass transfer of CO2 in the methylated oleic acid system was investigated, and a mathematical model was developed. The dissolution of CO2 was found to be exothermic, and the dissolution capacity decreases with increasing temperature and decreasing pressure. The solubility of CO2 follows an order of methylated form > epoxidized form > carbonated form. A high conversion rate (68.45 %) of epoxides was achieved in 6 h at 443.15 K and 3 MPa with a catalyst loading of 0.042 g·mL−1. These results show a potential route for synthesizing aliphatic carbonates by combining methyl oleate with CO2.

Zinc-aluminum mixed oxide nanocomposites catalyzed KA2 coupling of ketone, amine, and an alkyne: An environmentally benign approach

Heterogeneous catalysis is of prime importance especially to produce essential fine chemicals and organic molecules. Herein, we presented the simplest synthesis and application of zinc-aluminum mixed oxide nanocomposites (ZnAl-MO NCs) as an efficient catalyst for three component one-pot KA2 coupling reactions to prepare tetrasubstituted propargylamines. The as synthesized ZnAl-MO NCs were well characterized using spectroscopic tools viz. PXRD, BET, XPS, HRTEM, ICP techniques. ZnAl-MO NCs selectively catalyze the KA2 coupling reactions between ketone, amine and an alkyne affording wide range of functional substrates with higher conversion rates and yield. The sustainability of the catalyst was also studied systematically by evaluating the green chemistry metrics such as E factor, atom economy and turn over numbers. Notably, the architectures proposed methodology not only highlights the versatility of environmentally benign novel catalyst but also displays lower leaching levels for zinc and aluminum respectively.

Alumina supported platinum-ceria catalyst for reverse water gas shift reaction

The activation of CO2 molecules is a fundamental step for their effective utilization. Constructing high-density oxygen vacancies on the surface of reducible oxides is pivotal for the activation of CO2. In this work, we prepared a series of 0.5PtxCe/Al2O3 (x = 1, 5, 10, or 20) catalysts with varying Ce loading and 0.5 wt% of Pt for the reverse water gas shift (RWGS) reaction. The size of CeO2 particle increases with Ce loading. Remarkably, the 0.5Pt5Ce/Al2O3 catalyst with an average CeO2 particle size of 5.5 nm exhibits a very high CO2 conversion rate (116.4 × 10−5 molCO2/(gcat·s)) and CO selectivity (96.1%) at 600 °C. Our experimental findings reveal that the small-size CeO2 in 0.5Pt5Ce/Al2O3 possesses a greater capacity to generate reactive oxygen vacancies, promoting the adsorption and activation of CO2. In addition, the oxygen vacancies are cyclically generated and consumed during the reaction, which contributes to the elevated catalytic performance of the catalyst. This work provides a general strategy to construct rich oxygen vacancies on CeO2 for designing high-performance catalysts in C1 chemistry.

A novel endo-1,4-β-xylanase from Alicyclobacillus mali FL18: Biochemical characterization and its synergistic action with β-xylosidase in hemicellulose deconstruction

A novel endo-1,4-β-xylanase-encoding gene was identified in Alicyclobacillus mali FL18 and the recombinant protein, named AmXyn, was purified and biochemically characterized. The monomeric enzyme worked optimally at pH 6.6 and 80 °C on beechwood xylan with a specific activity of 440.00 ± 0.02 U/mg and a good catalytic efficiency (kcat/KM = 91.89 s−1mLmg−1). In addition, the enzyme did not display any activity on cellulose, suggesting a possible application in paper biobleaching processes. To develop an enzymatic mixture for xylan degradation, the association between AmXyn and the previously characterized β-xylosidase AmβXyl, deriving from the same microorganism, was assessed. The two enzymes had similar temperature and pH optima and showed the highest degree of synergy when AmXyn and AmβXyl were added sequentially to beechwood xylan, making this mixture cost-competitive and suitable for industrial use. Therefore, this enzymatic cocktail was also employed for the hydrolysis of wheat bran residue. TLC and HPAEC-PAD analyses revealed a high conversion rate to xylose (91.56 %), placing AmXyn and AmβXyl among the most promising biocatalysts for the saccharification of agricultural waste.

Risk of cancer and serious disease in Danish patients with urgent referral for serious non-specific symptoms and signs of cancer in Funen 2014–2021

BackgroundIn 2011, as the first European country, Denmark introduced the non-organ-specific cancer patient pathway (CPP) for patients presenting with non-specific symptoms and signs of cancer (NSSC). The proportion of patients with cancer over time is unknown.MethodsA retrospective cohort study of all patients with a NSSC-CPP investigational course in the province of Funen to the Diagnostic Centre in Svendborg from 2014 to 2021 was performed to evaluate the proportion of patients with cancer and serious disease over time.ResultsA total of 6698 patients were referred to the NSSC-CPP of which 20.2% had cancer. While the crude referral rate increased from 114 per 100,000 people in 2014 and stabilised to around 214 in 2017–2021, the cancer detection rate of the total yearly new cancers in Funen diagnosed through the NSSC-CPP in DC Svendborg increased from 3 to 6%.ConclusionsWith now high and stable conversion and crude referral rates, the NSSC-CPP is one of the largest CPPs in Denmark as measured by the number of new cancer cases found. Similar urgent referral programmes in other countries might fill an unmet medical need for patients presenting with serious non-specific symptoms and signs of cancer in general practice.

Farm factors influencing spatial variations of cropland use and change in the context of urban expansion: The case of Jimma City, Southwest Ethiopia

Urban factors comprising economic and population growth are widely discussed as determinants of cropland-use change decisions and urbanization containment. Despite the academic discussion, farm factors remain detached from urban planning theories and practices. This study used a cross-sectional survey and remote sensing data to investigate farm factors influencing farmers’ cropland-use decisions. To measure human farm factors, a structured questionnaire was used to collect quantitative data from a randomly selected 300 farmers in Jimma peri-urban areas while an unstructured questionnaire was used to gather views of conveniently recruited participants. Landsat-8 and the Digital Elevation Model (DEM) were employed to extract the physical factors. The Ordinary Least Squares (OLS) model was used to determine significant farm factors of cropland-use decisions and the Geographical Weighted Regression (GWR) model was applied to map the spatial variation in cropland-use decisions along the rural-urban continuum. The results revealed that farm factors influenced the cropland-use decisions of farmers. Cropland-use conversion rates increase with distance to the urban center due to greater access to social services. The conversion rates also increase with decreasing slope gradients and good soil quality. Farmers with higher farm income, labour, and extension have lower cropland-use conversion rates while those with higher non-farm income and labour, family size, farm size, and education have higher conversion rates. The findings of this study suggest that government policies aimed at restricting urban growth and sustaining ecosystem services should adopt farm factors to preserve prime cropland-use along the rural-urban continuum. Considering farm factors in urban land-use planning also promotes synergistic rural-urban planning integrations to bring balanced rural-urban development, poverty reduction, slow urban migration, and smart urban growth.

The energy-converting hydrogenase Ech2 is important for the growth of the thermophilic acetogen Thermoanaerobacter kivui on ferredoxin-dependent substrates.

Acetogens thrive by converting H2+CO2 to acetate. Under environmental conditions, this allows for only very little energy to be conserved (∆G'<-20 kJ mol-1). CO2 serves as a terminal electron acceptor in the ancient Wood-Ljungdahl pathway (WLP). Since the WLP is ATP neutral, energy conservation during growth on H2 + CO2 is dependent on the redox metabolism. Two types of acetogens can be distinguished, Rnf- and Ech-type. The function of both membrane-bound enzyme complexes is twofold-energy conversion and redox balancing. Ech couples the Fd-dependent reduction of protons to H2 to the formation of a proton gradient in the thermophilic bacterium Thermoanaerobacter kivui. This bacterium may be utilized in gas fermentation at high temperatures, due to very high conversion rates and the availability of genetic tools. The physiological function of an Ech hydrogenase in T. kivui was studied to contribute an understanding of its energy and redox metabolism, a prerequisite for future industrial applications.

Constructing and characterizing various multi-component crosslinked epoxy resins based on molecular dynamics simulations with a curing reaction model

Epoxy resins are extensively used as the matrix for carbon-fiber-reinforced plastic (CFRP) in commercial airplanes due to their outstanding thermomechanical properties. Until now, few researchers have simulated multicomponent epoxy resins. In this work, the impact of stoichiometric variations in the base resins in the Di Glycidyl Ether of Bisphenol A (DGEBA)/Tetra Glycidyl Diamino Diphenyl Methane (TGDDM)/4,4′-Diamino Diphenyl Sulfone (4,4′-DDS) system on the curing process and thermomechanical properties is investigated. When the proportions of each component are comparable, the curing process is primarily determined initially by the component with a lower activation energy and subsequently by the component with a relatively greater quantity during the high conversion rate stage. Furthermore, a higher proportion of TGDDM in the DGEBA/TGDDM/4,4′-DDS system results in an increased number of ring structures, which in turn leads to enhanced thermomechanical properties. Our Python-LAMMPS algorithm can be further developed for designing new multi-component epoxy resin materials.

Synthesis, Structural and Redox Properties of Vanadyl β‐Cyanoporphyrin and its Utilization as Efficient Catalyst for Epoxidation of Olefins and Oxidative Bromination of Phenols

Abstract2‐Cyano‐5,10,15,20‐tetraphenylporphyrin [H2TPPCN] (1) having cyano group at one of β‐pyrrolic positions using nucleophilic substitution reaction of tetrabutylammonium cyanide (TBACN) on free‐base 2‐nitro‐5,10,15,20‐tetraphenylporphyrin, and its oxidovanadium(IV) complex [VIVOTPPCN] (2) were synthesized in good yields. Both the porphyrins 1 and 2 have been characterized by UV‐Vis spectroscopy, mass spectrometry, and cyclic voltammetric techniques. Single crystal X‐Ray crystallography revealed quasi‐planar geometry for 1. Compounds 1 and 2 exhibited a red shift (λmax=7–9 nm) in the Soret band relative to [MTPP], where M=2H, VIVO owing to the electron‐withdrawing effect of the cyano group at the β‐position. The first oxidation (ΔE1/2=110–140 mV) and reduction potentials (ΔE1/2=220–260 mV) of 1 and 2 are anodically shifted relative to [MTPP] where M=2H, VIVO. Porphyrin 2 has been utilized as a catalyst for two reactions: epoxidation of olefins and bromination of phenols. The bromination of phenol using KBr/H2O2/HClO4 in water resulted in 100 % conversion with a TOF value as high as 19.6 s−1 in 0.5 h. Using H2O2/NaHCO3 in a CH3CN/H2O solvent mixture at 60 °C, epoxidation was carried out, and the highest conversion rate with a turnover frequency of 1.9 s−1 was achieved in the case of cyclohexene. Catalyst 2 was recovered successfully at the end of the reaction up to 5 cycles and had good thermal stability, indicating its industrial viability and applicability. Moreover, these cyano‐functionalized porphyrins could be further utilized for the generation of molecular self‐assemblies, post‐functionalization of porphyrin core and various applications. The current findings in this work present insights for a facile approach for the synthesis of β‐cyano functionalized porphyrin 1 and further shed light on the utility of its vanadyl complex 2 as an efficient catalyst for olefin epoxidation and phenol bromination reactions.

A population of faint, old, and massive quiescent galaxies at 3

Here we present a sample of 12 massive quiescent galaxy candidates at z∼3-4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$z\\sim 3-4$$\\end{document} observed with the James Webb Space Telescope (JWST) Near Infrared Spectrograph (NIRSpec). These galaxies were pre-selected from the Hubble Space Telescope imaging and 10 of our sources were unable to be spectroscopically confirmed by ground based spectroscopy. By combining spectroscopic data from NIRSpec with multi-wavelength imaging data from the JWST Near Infrared Camera (NIRCam), we analyse their stellar populations and their formation histories. We find that all of our galaxies classify as quiescent based on the reconstruction of their star formation histories but show a variety of quenching timescales and ages. All our galaxies are massive (∼0.1-1.2×1011\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sim 0.1-1.2\ imes 10^{11}$$\\end{document} M⊙\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_\\odot$$\\end{document}), with masses comparable to massive galaxies in the local Universe. We find that the oldest galaxy in our sample formed ∼1.0×1011\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sim 1.0\ imes 10^{11}$$\\end{document} M⊙\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_\\odot$$\\end{document} of mass within the first few hundred million years of the Universe and has been quenched for more than a billion years by the time of observation at z∼3.2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$z\\sim 3.2$$\\end{document} (∼2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sim 2$$\\end{document} billion years after the Big Bang). Our results point to very early formation of massive galaxies requiring a high conversion rate of baryons to stars in the early Universe.

Seller promotion and competition on decentralized two-sided platforms

PurposeThis paper aims to explore the promotion decisions of heterogeneous sellers on a decentralized platform under competitive conditions and analyze how seller behaviors impact platform profit, seller revenue, buyer surplus and social welfare.Design/methodology/approachThis paper considers a Cournot model consisting of a platform charging a commission rate and two sellers with different conversion rates and browsing costs. Promotion efforts by sellers can increase traffic, but they also incur promotion costs for sellers. The sellers decide on promotion effort by weighing these two effects. The authors also explore the equilibrium when the platform charges a fixed usage fee.FindingsThe seller’s profit improves as its conversion rate increases and worsens as browsing costs increase. Also, increasing the commission rate charged by the platform makes the seller invest less in promotional efforts. Therefore, the platform must consider this trade-off to determine an optimal rate. The analysis shows that the seller with a high conversion rate and high browsing cost plays a greater role in generating more overall revenue. When the market favors such a seller, the platform tends to charge less in order not to impair its profitability.Originality/valueThis paper incorporates conversion rate, buyer’s browsing cost, unit promotion cost and the fee charged by the platform into the model to study sellers’ promotion decisions on decentralized platforms.