Constrained Representations of Map Graphs and Half-Squares

The square of a graph H, denoted H^2, is obtained from H by adding new edges between two distinct vertices whenever their distance in H is two. The half-squares of a bipartite graph B=(X,Y,E_B) are the subgraphs of B^2 induced by the color classes X and Y, B^2[X] and B^2[Y]. For a given graph G=(V,E_G), if G=B^2[V] for some bipartite graph B=(V,W,E_B), then B is a representation of G and W is the set of points in B. If in addition B is planar, then G is also called a map graph and B is a witness of G [Chen, Grigni, Papadimitriou. Map graphs. J. ACM49 (2) (2002) 127-138]. While Chen, Grigni, Papadimitriou proved that any map graph G=(V,E_G) has a witness with at most 3|V|-6 points, we show that, given a map graph G and an integer k, deciding if G admits a witness with at most k points is NP-complete. As a by-product, we obtain NP-completeness of edge clique partition on planar graphs; until this present paper, the complexity status of edge clique partition for planar graphs was previously unknown. We also consider half-squares of tree-convex bipartite graphs and prove the following complexity dichotomy: Given a graph G=(V,E_G) and an integer k, deciding if G=B^2[V] for some tree-convex bipartite graph B=(V,W,E_B) with |W|<=k points is NP-complete if G is non-chordal dually chordal and solvable in linear time otherwise. Our proof relies on a characterization of half-squares of tree-convex bipartite graphs, saying that these are precisely the chordal and dually chordal graphs

Complexity results for matching cut problems in graphs without long induced paths

In a graph, a (perfect) matching cut is an edge cut that is a (perfect) matching. Matching Cut (MC), respectively, Perfect Matching Cut (PMC), is the problem of deciding whether a given graph has a matching cut, respectively, a perfect matching cut. The Disconnected Perfect Matching problem (DPM) is to decide if a graph has a perfect matching that contains a matching cut. Solving an open problem recently posed in [Lucke, Paulusma, Ries (ISAAC 2022), and Feghali, Lucke, Paulusma, Ries (arXiv:2212.12317)], we show that PMC is NP-complete in graphs without induced 14-vertex path $P_{14}$. Our reduction also works simultaneously for MC and DPM, improving the previous hardness results of MC on $P_{19}$-free graphs and of DPM on $P_{23}$-free graphs to $P_{14}$-free graphs for both problems. Actually, we prove a slightly stronger result: within $P_{14}$-free graphs, it is hard to distinguish between (i) those without matching cuts and those in which every matching cut is a perfect matching cut, (ii) those without perfect matching cuts and those in which every matching cut is a perfect matching cut, and (iii) those without disconnected perfect matchings and those in which every matching cut is a perfect matching cut. Moreover, assuming the Exponential Time Hypothesis, none of these problems can be solved in time $2^{o(n)}$ for $n$-vertex $P_{14}$-free input graphs. We also consider the problems in graphs without long induced cycles. It is known that MC is polynomially solvable in graphs without induced cycles of length at least 5 [Moshi (JGT 1989)]. We point out that the same holds for DPM.Comment: To appear in the proceedings of WG 202

Factors Affecting Responsibility Accounting: Evidence from Vietnamese Manufacturing Enterprises

Purpose: This study aims to examine (i) the number of product lines and steps in the manufacturing process affect the responsibility cost center in a responsibility accounting system (ii) the level of technology application, the qualification of managers at all levels affect the budgetary control system integrated to the responsibility accounting system in Vietnamese manufacturing enterprises.   Theoretical framework: The research identifies and examined the impacts of the number of product lines, the number of steps in the manufacturing process on the number of responsibility cost centers, and the impacts of the level of technology application, the qualification of managers at all levels on the budgetary control system to contribute the responsibility accounting system theory.   Design/methodology/approach:  A quantitative approach was applied with a sample of 108 Vietnamese manufacturing enterprises that is listed on the Vietnamese financial securities markets in 2020. OLS regression is applied to give a further analysis.   Findings: The regression findings support the significant positive impacts of the number of product lines and the number of steps in the manufacturing process on the number of cost centers as well as the significant positive correlation between the level of technology application and the effective budgetary control system, however, the effect of the qualification of managers at all levels is insignificant.   Research, Practical &amp; Social implications: This study provides factors impacting the number of cost centers and the budgetary control system. The results of this study support the contingency theory.   Originality/value: These findings can be useful for Vietnamese manufacturing enterprises to take measures to strengthen cost control through the responsibility accounting system, thereby improving business efficiency

Analysing the loan loss provisioning and efficiency of the banks in Vietnam

This study examines the loan loss provision practices of banks in Vietnam to see whether its behaviours follows the business cycle, or subjects to the management objectives with regards to earnings management and capital management. In addition, a relationship between banks’ efficiency and their level of provisioning for loan losses is also studied. Using the accounting data of 38 commercial banks in Vietnam from 2006 to 2011, the estimates of efficiencies’ level of all the banks sampled were obtained from the stochastic input distance function. These efficiency scores would then be incorporated into the regression of loan loss provision against other explanatory variables. The estimated results from Generalised Moments of Method (GMM) estimators suggest that banks in Vietnam do not use loan loss provision to smooth income or manage regulatory capital. However, the provisioning practice is found to follow procyclicality because loan loss provision is negatively correlated with earnings, and GDP growth. Moreover, loan loss provision is found to be positively correlated with gross loans and size. Furthermore, efficiency can significantly explain the behaviour of loan loss provision in Vietnam in a way that banks with higher efficiency level would have lower loan loss provision

Antimicrobial and antioxidant activity of bacterial endophytes isolated from leaves of the mangrove plant Rhizophora stylosa

Mangroves are the most productive ecosystems and contain highly diverse plants and microbial communities. Mangrove endophytes are proved to be a rich source of bioactive secondary metabolites. The biological molecules produced by endophytes play an important role in protection of mangrove plants against herbivores, insects as well as pathogens. The present study aimed to isolate the endophytic bacteria from the mangrove plant Rhizophora stylosa and screen antimicrobial and antioxidant activity of ethyl acetate extracts from the isolated endophytic bacteria. A total of 64 endophytic bacterial strains from R. stylosa leaves were isolated, of which ethyl acetate extracts of 14 isolated endophytic strains showed antimicrobial activity against at least one of reference microorganisms Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 25923, Bacillus subtilis ATCC 27212, Staphylococcus aureus ATCC 12222 and Candida albicans ATCC 7754 with MIC values from 32 to 512 µg/ml. Among them, four strains showed activity against one reference microorganism, five strains showed activity against two reference microorganisms, four strains showed activity against three reference microorganisms, and one strain showed activity against four reference microorganisms. Additionally, the ethyl acetate extracts of 12 isolated endophytic bacteria showed ATBS and DPPH radical scavenging activity with scavenging values from 36.27 ± 2.6% to 71.46 ± 6.6% and from 26.22 ± 3.3% to 57.38 ± 5.8%, respectively. The identification of the five most active endophytic bacteria by 16S rRNA sequences revealed that the endophytes belonged to four genera, including Bacillus, Streptomyces, Pseudovibrio and Pseudomonas. The obtained results suggest that the endophytic bacteria from mangrove plants are a promising reservoir of antimicrobial and antioxidant agents.      

STUDENTS' PERCEPTION OF THE INFLUENCE OF INTONATION IN ENGLISH ON CONVEYING THE MEANING OF SPEECH IN COMMUNICATION

In communication, intonation plays an important role in conveying the meaning of a speech. In this article, we study students' perception of the influence of intonation in conveying the meaning of speech in communication to propose solutions to help students overcome intonation errors when communicating, as well as, help teachers have appropriate intonation teaching methods. Our data and analysis are based on research documents, surveys, and in-depth interviews with students. According to the study results, most students are well aware of the importance of intonation and of the factors affecting intonation, and they are also aware of the causes of intonation errors. However, students do not apply their knowledge of intonation to speech, they stop at the cognitive level. The study indicates that students often make intonation mistakes in Tag-question, Wh-question, and Imperative sentence in communication.  Article visualizations