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摘要： Fructooligosaccharides (FOS) are widely recognized prebiotics that selectively stimulate beneficial gut microbiota. Among short-chain FOS, 1-kestose has been reported to exert superior bifidogenic activity compared to longer-chain oligosaccharides, and its enrichment in FOS mixtures is increasingly valued for therapeutic and nutritional applications. However, industrial production of FOS from sucrose often results in mixtures contaminated with residual sucrose and glucose, which diminish prebiotic efficacy and limit use in populations with metabolic disorders. To address this, we developed a recombinant Komagataella phaffii strain expressing a mutated levansucrase (LsdA R171K–H172S) from Gluconoacetobacter diazotrophicus for the synthesis and purification of FOS. Fed-batch culture experiments revealed an imbalance between periplasmic retention and extracellular secretion of the enzyme, despite the presence of a secretion signal. To overcome this limitation, cells were immobilized in calcium alginate beads, enabling simultaneous sucrose hydrolysis and glucose consumption. Optimal biomass loading was determined to be 300 g/L, balancing enzymatic activity and bead stability. Semicontinuous purification was performed in a fixed column at 35 °C with varying carbohydrate concentrations. The highest FOS purity (91.8%) and recovery (90.5%) were achieved at 400 g/L carbohydrate concentration. The resulting solution contained predominantly 1-kestose (79.9%) with 20% nystose, and negligible residual sucrose or glucose. This one-step bioprocess demonstrates an efficient strategy for producing high-purity FOS enriched in 1-kestose, offering advantages over conventional fermentation and purification methods and supporting the development of functional foods with enhanced prebiotic potential.

关键词： 1-Propanol   Culture-dependent validation   Environmental factors   Metabolic pathways   Metagenomics   Microbial community  

摘要： 1-Propanol is a crucial flavor compound in Jiang-flavor Baijiu, yet the key microbial pathways and environmental factors controlling its synthesis have not been systematically investigated. Using an integrated approach of metagenomics and culture-dependent techniques, this study identified the key microbes, pathways, and factors controlling 1-propanol synthesis. The highest 1-propanol level was detected in first-round base Baijiu, with rapid accumulation during early pit fermentation. Metagenomics revealed the propanoate pathway as the dominant route, primarily contributed by Limosilactobacillus, while Pichia and Saccharomyces were key providers of pyruvate decarboxylase in the citramalate and threonine pathways. Pure-culture validation confirmed that L. panis MR32 predominantly utilizes 1,2-propanediol as the precursor, while yeasts such as P. kudriavzevii 2J2 and S. cerevisiae LB7A prefer the 2-ketobutyrate pathway. Environmental tests revealed optimal 1-propanol production by L. panis MR32 at pH 5.5 and increasing yields with temperature (25–45 °C). In contrast, most yeasts produced the most 1-propanol at 30 °C, beyond which yields declined, with only P. kudriavzevii 2J2 and I. orientalis IO tolerating high lactic acid. Our findings clarify the microbial division of labor and environmental drivers of 1-propanol formation, enabling targeted fermentation control.

关键词： Cycle   Stability   Turán number  

摘要： Starting from the stability theorem of Erdős and Simonovits, there have been interesting studies on stability of graphs forbidding certain substructures in terms of edge numbers, minimum degrees or numbers of cliques. In this paper we obtain strong structural stability of $C_{2k+1}$-free in terms of the number of copies of $C_4$. Let $\mathcal{N}(F,G)$ be the number of copies of F in G. We show that a $C_{2k+1}$-free graph G must be very close to $K_{\lfloor \frac{n}{2}\rfloor ,\lceil \frac{n}{2}\rceil }$ when

来源 ScienceDirectJournal 详细信息

关键词： Bivariate exponential distribution   Correlated queues   Customer abandonment   Markov modulated fluid flow process  

摘要： This paper analyzes a single-server queueing system that integrates correlated interarrival and service processes with customer abandonment, which is a challenging combination that has remained largely unaddressed in the queueing literature due to the analytical difficulties of modeling these features simultaneously. Such queueing systems have many applications in telecommunications networks, service systems (e.g., call centers), and healthcare (e.g., emergency department), where both correlation and abandonment play critical roles. In the queueing system, interarrival and service times are modeled using a bivariate exponential distribution, which captures any possible dependencies between them. Customers may abandon the system if their sojourn/waiting time exceeds a random patience threshold, which follows a general discrete distribution. We employ a multi-layer Markov-modulated fluid flow (MMFF) process to characterize the evolution of the age of the customer in service. Through this framework, we derive closed-form expressions for key performance metrics, including sojourn time distributions, abandonment probabilities, and the probability distribution of queue length, which goes beyond the mean and variance typically provided by MMFF theory. We develop efficient recursive algorithms for computing these distributions, making the results practically implementable. Furthermore, we analyze the impact of the correlation coefficient on system performance, offering managerial insights into how dependency structures affect operational outcomes. Numerical results indicate that increasing the correlation between interarrival times and service times does not always result in a shorter queue.

关键词： 1,5-Diamino-2-hydroxypentane   3-Hydroxylysine   l-lysine 3-hydroxylase   l   SpLDC   Pathway enhancement  

摘要： 1,5-Diamino-2-hydroxypentane (2-OH-PDA) is a novel aliphatic β-amino alcohol with potential for a wide range of applications, and its efficient and green synthesis has attracted increasing attention. In this study, we developed a biosynthetic pathway for 2-OH-PDA from glucose. Firstly, the Fe²⁺/α-ketoglutarate (α-KG)-dependent l-Lysine-3-hydroxylase (K3H) was heterologously expressed in E coli NT1003 capable of highly producing l-lysine to construct a biosynthetic pathway strain of 3-hydroxylysine (3-OH-lysine). By intensifying the pathway, introducing a glutamate oxidation system, and optimizing the fermentation conditions, 40.2 g/L 3-OH-lysine were achieved in the fed-batch fermentation. Then, lysine decarboxylase (SpLDC) was used to catalyze the decarboxylation of 3-OH-lysine to 2-OH-PDA, yielding 29.2 g/L with a molar conversion efficiency of 99.7%. This study provides an economical, efficient and green route for the biosynthesis of 2-OH-PDA.

关键词： 1,3-Diketo   Jigsaw puzzle method   Mechano-chemistry   Radical  

摘要： Antiwear additives without S and P are often misinterpreted: their antifriction and antiwear effects are frequently attributed to adsorption, overlooking the role of mechanochemistry. A pertinent example is 1,3-diketo compounds, which have been reported to achieve macroscopic superlubricity since 2013, with their lubricity traditionally explained by chelation-driven adsorption on metal surfaces. In contrast, we demonstrate that radical-mediated mechanochemistry is the primary mechanism. Specifically, the keto tautomer of 1,3-diketo compounds serves as a radical initiator, while the enol tautomer functions as a monomer. Under friction, homolysis weak C–C bond in the keto tautomer generates radicals, which initiate polymerization at the CC double bonds of the enol tautomer, ultimately forming a protective tribofilm that reduces friction and wear. This interpretation is based on our “jigsaw puzzle method”, that molecules connected by two stabilized radicals can exhibit mechano-chemical activity. Guided by this mechanism, we designed a compounded system comprising a keto-tautomer-only 1,3-diketo molecule and the double-bond-containing molecule oleic acid. This formulation exhibits antiwear performance about two orders of magnitude better than that of commercial formulated oils. This work calls for broader investigation beyond adsorption, especially on mechano-chemistry, when studying lubrication mechanisms.

关键词： 1,3-Benzoxazin-4-one   Flash vacuum pyrolysis   Diels-Alder reaction  

摘要： Gas phase thermal elimination of ethanol from 2-ethoxy-2,3-dihydro-1,3-benzoxazin-4-one 2 leads to formation of 1,3-benzoxazin-4-one 3 allowing its characterisation by ¹H and ¹³C NMR for the first time. The compound is highly moisture sensitive and its hydrolysis product, N-formylsalicylamide 8, shows an interesting and complex pattern of hydrogen bonding in the X-ray crystal structure. Reaction with other nucleophiles such as amines leads to ring-opened N-acylformamidines. The compound undergoes BF₃•Et₂O catalysed Diels-Alder reaction with electron-rich dienes such as 2,3-dimethylbutadiene, cyclohexa-1,3-diene, penta-1,3-diene and 2-methylbuta-1,3-diene in CH₂Cl₂ to give a low yield of cycloadducts which were fully characterised by NMR. The same products may also be obtained, in agreement with an earlier study, by reaction of the 2-ethoxy precursor 2 with BF₃•Et₂O in diethyl ether in the presence of 1,3-dienes. In the case of 2-methyl-1,3-butadiene the product of an ene reaction was also observed.

关键词： 阿尔茨海默病   沉默信息调节因子1   能量代谢   氧化应激   神经源性炎症   突触可塑性   中药   研究进展  

摘要： 背景:沉默信息调节因子1作为一种去乙酰化酶,其激活后可调节多种蛋白的转录活性以及许多阿尔茨海默病相关病理过程,包括调节能量代谢、氧化应激、神经炎症、自噬和细胞凋亡等,与阿尔茨海默病的发生、发展及转归密切相关。近年来,大量研究发现,中药单体有效成分及复方可通过激活沉默信息调节因子1信号通路,减少细胞凋亡、保护神经元、抑制淀粉样斑块形成等病理改变,延缓阿尔茨海默病的发展。目的:探讨沉默信息调节因子1与阿尔茨海默病的关系及中药调控沉默信息调节因子1信号通路治疗阿尔茨海默病的作用机制。方法:以“阿尔茨海默病,痴呆,炎症,沉默信息调节因子1,氧化应激,炎症因子,信号通路,中药单体,复方”为中文检索词,“Alzheimer’s disease,dementia,SIRT1,inflammation,oxidative stress,inflammatory factors,signaling pathways,TCM monomers,compounds”为英文检索词,检索2015年1月至2025年3月中国知网、万方、维普、中国生物医学文献数据库(SinoMed)和PubMed数据库发表的有关沉默信息调节因子1与阿尔茨海默病及中药调控机制的文献,排除与文章相关性不高及重复、过时的文献,共检索出4921篇相关文献,最终纳入154篇文献进行综述。结果与结论:①大量实验研究证实,沉默信息调节因子1在阿尔茨海默病中具有重要作用;②中医方药可通过多种方式调节沉默信息调节因子1信号通路,如阿魏酸钠通过提高阿尔茨海默病大鼠前额叶皮质区沉默信息调节因子1的表达,而改善因缺血缺氧受损的神经细胞,进而改善阿尔茨海默病大鼠的学习记忆能力;牡蛎肽能够增强活性氧,降低海马组织的氧化损伤,缓解神经炎症,增强突触功能,减少神经元损伤和死亡,发挥脑保护作用,改善认知功能障碍。

关键词： Fuzzy implication   Ordinal sum   Pre-aggregation function   Pre-quasi-pseudo grouping function   Pre-quasi-pseudo overlap function  

摘要： The r→-(quasi)-overlap (grouping) functions can be seen as a generalization of the overlap (grouping) functions from “aggregation” to “pre-aggregation”. The relaxation of monotonicity condition leads to better performance in classification problems. Actually, in addition to monotonicity, the commutativity in the definition is also a restrictive condition, as it requires the objects under discussion to be of equal importance. However, asymmetry is prevalent in practical applications, such as distinguishing foreground from background in image processing. On the other hand, fuzzy implications closely related to overlap (grouping) functions and their extensions are crucial in applications such as fuzzy control. Nevertheless, fuzzy implication operators induced by non-commutative pre-quasi-overlap (grouping) functions remains unexplored. Therefore, this article introduces and analyzes the pre-quasi-pseudo overlap (grouping) functions and related residuated implications. First, we consider the extension of pre-quasi-pseudo overlap (grouping) functions on bounded partially ordered sets and propose the concepts of C-monotone quasi-pseudo overlap (grouping) functions. Then induced conditioned monotonic residuated (co-)implications are defined, and related properties are presented. In particular, the ordinal sum and other construction methods of C-monotone quasi-pseudo overlap (grouping) functions are given. Second, the notions of R-monotone quasi-pseudo overlap (grouping) functions are put forward, and their construction theorems as well as the induced directional monotonic residuated (co-)implications are discussed. Moreover, some results regarding the residual principle are demonstrated. The functions introduced in the paper have a broader range of applications and are expected to perform better in classification and image processing. © The Author(s) under exclusive licence to Sociedade Brasileira de Matemática Aplicada e Computacional 2026.