146 research outputs found
Integer colorings with forbidden rainbow sums
For a set of positive integers , an -coloring of is
rainbow sum-free if it contains no rainbow Schur triple. In this paper we
initiate the study of the rainbow Erd\H{o}s-Rothchild problem in the context of
sum-free sets, which asks for the subsets of with the maximum number of
rainbow sum-free -colorings. We show that for , the interval is
optimal, while for , the set is optimal. We
also prove a stability theorem for . The proofs rely on the hypergraph
container method, and some ad-hoc stability analysis.Comment: 20 page
The minimum positive uniform Tur\'an density in uniformly dense -uniform hypergraphs
A -graph (or -uniform hypergraph) is uniformly dense if the edge
distribution of is uniformly dense with respect to every large collection
of -vertex cliques induced by sets of -tuples. Reiher, R\"odl and
Schacht [Int. Math. Res. Not., 2018] proposed the study of the uniform Tur\'an
density for given -graphs in uniformly dense -graphs.
Meanwhile, they [J. London Math. Soc., 2018] characterized -graphs
satisfying and showed that ``jumps" from 0
to at least . In particular, they asked whether there exist -graphs
with equal or arbitrarily close to . Recently, Garbe,
Kr\'al' and Lamaison [arXiv:2105.09883] constructed some -graphs with
.
In this paper, for any -graph , we give a lower bound of
based on a probabilistic framework, and provide a general theorem that reduces
proving an upper bound on to embedding in reduced -graphs
of the same density using the regularity method for -graphs. By using this
result and Ramsey theorem for multicolored hypergraphs, we extend the results
of Garbe, Kr\'al' and Lamaison to . In other words, we give a
sufficient condition for -graphs satisfying .
Additionally, we also construct an infinite family of -graphs with
.Comment: 25 page
Existence of Local Saddle Points for a New Augmented Lagrangian Function
We give a new class of augmented Lagrangian functions for nonlinear
programming problem with both equality and inequality constraints. The close relationship
between local saddle points of this new augmented Lagrangian and local optimal
solutions is discussed. In particular, we show that a local saddle point is a local optimal
solution and the converse is also true under rather mild conditions
Hypergraphs with a quarter uniform Tur\'an density
The uniform Tur\'an density of a -uniform hypergraph is
the supremum over all for which there is an -free hypergraph with the
property that every linearly sized subhypergraph with density at least .
Determining for given hypergraphs was suggested by Erd\H{o}s
and S\'os in 1980s. In particular, they raised the questions of determining
and . The former question was solved
recently in [Israel J. Math. 211 (2016), 349-366] and [J. Eur. Math. Soc. 20
(2018), 1139-1159], while the latter is still a major open problem. In addition
to , there are very few hypergraphs whose uniform Tur\'an density
has been determined.
In this paper, we give a sufficient condition for -uniform hypergraphs
satisfying . In particular, currently all known -uniform
hypergraphs whose uniform Tur\'an density is , such as and
the -uniform hypergraphs studied in [arXiv:2211.12747],
satisfy this condition. Moreover, we find some intriguing -uniform
hypergraphs whose uniform Tur\'an density is also .Comment: 23 page
Influence of Helicobacter pylori culture supernatant on the ecological balance of a dual-species oral biofilm
Dental caries is a chronic progressive disease occurring in the tooth hard tissue due to multiple factors, in which bacteria are the initial cause. Both Streptococcus mutans and Streptococcus sanguinis are main members of oral biofilm. Helicobacter pylori may also be detected in dental plaque, playing an important role in the development of dental caries. Objective The aim of this study was to investigate the effect of H. pylori culture supernatant on S. mutans and S. sanguinis dual-species biofilm and to evaluate its potential ability on affecting dental health. Material and methods The effect of H. pylori supernatant on single-species and dual-species biofilm was measured by colony forming units counting and fluorescence in situ hybridization (FISH) assay, respectively. The effect of H. pylori supernatant on S. mutans and S. sanguinis extracellular polysaccharides (EPS) production was measured by both confocal laser scanning microscopy observation and anthrone-sulfuric acid method. The effect of H. pylori supernatant on S. mutans gene expression was measured by quantitative real-time PCR (qRT-PCR) assays. Results H. pylori supernatant could inhibit both S. mutans and S. sanguinis biofilm formation and EPS production. S. sanguinis inhibition rate was significantly higher than that of S. mutans. Finally, S. mutans bacteriocin and acidogenicity related genes expression were affected by H. pylori culture supernatant. Conclusion Our results showed that H. pylori could destroy the balance between S. mutans and S. sanguinis in oral biofilm, creating an advantageous environment for S. mutans, which became the dominant bacteria, promoting the formation and development of dental caries
Teachers’ experiences of developing the teacher-student relationships during COVID-19 in China
The purpose of this study was to express middle school teachers’ experiences of developing teacher-student relationships (TSRs) in online teaching during COVID-19 in China. The study used a qualitative phenomenological design to offer an in-depth description of the experience’s teachers perceive as strategies to develop TSRs. Participants (N=6) were from several middle schools in Nanning, GuangXi, China. Information was collected with semi-structured interviews and analyzed using a five-step phenomenological method in mental research. Data analysis revealed five general themes about teachers’ experiences. The study found that teachers’ proactively initiating dialogues, responding to student needs, emotion-based information exchange, treating students with respect, and expressing motivation and expectations for students were the strategies to develop TSRs. The results of this study can be used in middle school to create positive interventions to enhance educators’ understanding of strategies associated with TSRs
Cloning of a gene encoding glycosyltransferase from Pueraria lobata (Wild.) Ohwi and its expression in Pichia pastoris
The key enzyme of puerarin biosynthesis in Pueraria lobata (Willd.) Ohwi was unclear but may involve glycosylation. To investigate the regulation of puerarin biosynthesis, a putative UDP-dependent glycosyltransferase (UGT) gene, PlUGT1 was isolated from P. lobata root, which contained abundant puerarin. PlUGT1 encoded 480 deduced amino acid residues with a conserved UDP-glucose-binding domain, which has 61 to 84% similarity to homologues from other plant species. SDS polyacrylamide gel electrophoresis and western blotting results showed that, fusion protein migrated as a single protein band with a molecular weight of 55 kDa. A yeast expression vector pPICZA-PlUGT1 was constructed and was transformed into Pichia pastoris strain GS115. Several recombinants containing multi-copy expression cassettes were obtained on the zeocin-YPD plate and confirmed by southern dot blotting. The yield of PlUGT1 attained 0.05 g/l when recombinant cells were cultured at pH 5.5, 30°C and induced with 0.5% methanol for 72 h. The expression of PlUGT1 protein correlates positively with the copy numbers of PlUGT1 in transformed yeast cells. These results suggest that, the PlUGT1 protein can be expressed efficiently in the P. pastoris expression system and may supply a new economic and convenient way for the production of PlUGT1 protein.Keywords: Pueraria lobata (Willd.) Ohwi, glycosyltransferase, cloning, expression, Pichia pastori
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