In this paper, we characterize graphs whose tensor product admit nowhere‐zero 3‐flow. The main result is: For two graphs G1 and G2 with δurn:x-wiley:03649024:media:JGT20211:tex2gif-inf-3 ≥ 2 and G2 not belonging to a well‐characterized class of graphs, the tensor product of G1 and G2 admits a nowhere‐zero 3‐flow.

For a connected graph , an edge set is a k-restricted-edge-cut, if is disconnected and every component of has at least k vertices. The k-restricted-edge-connectivity of G, denoted by , is defined as the cardinality of a minimum k-restricted-edge-cut. The k-isoperimetric-edge-connectivity is defined as , where is the set of edges with one end in U and the other end in ⧹. In this note, we give some degree conditions for a graph to have optimal and/or .

Because of its application in the field of security in wireless sensor networks, k-path vertex cover (VCPk) has received a lot of attention in recent years. Given a graph G=(V,E), a vertex set C⊆V is a k-path vertex cover (VCPk) of G if every path on k vertices has at least one vertex in C, and C is a connected k-path vertex cover of G (CVCPk) if furthermore the subgraph of G induced by C is connected. A homogeneous wireless sensor network can be modeled as a unit disk graph. This paper presents a new PTAS for MinCVCPk on unit disk graphs. Compared with previous PTAS given by Liu et al., our method not only simplifies the algorithm and reduces the time-complexity, but also simplifies the analysis by a large amount.

A vertex set F is a k-path vertex cover () of graph G if every path of G on k vertices contains at least one vertex from F. A graph G is a d-dimensional ball graph if each vertex of G corresponds to a ball in , two vertices are adjacent in G if and only if their corresponding balls have nonempty intersection. The heterogeneity of a ball graph is defined to be , where and are the largest radius and the smallest radius of those balls, respectively. In this paper, we present a PTAS for the minimum problem in a ball graph whose heterogeneity is bounded by a constant.

Despite the increasing popularity and successful examples of crowdsourcing, its openness overshadows important episodes when elaborate sabotage derailed or severely hindered collective efforts. A service exchange dilemma arises when non-cooperation among self-interested users, and zero social welfare is obtained at myopic equilibrium. Traditional rating protocols are not effective to overcome the inefficiency of the socially undesirable equilibrium due to specific features of crowdsourcing: a large number of anonymous users having asymmetric service requirements, different service capabilities, and dynamically joining/leaving a crowdsourcing platform with imperfect monitoring. In this paper, we develop the first game-theoretic design of the two-sided rating protocol to stimulate cooperation among self-interested users, which consists of a recommended strategy and a rating update rule. The recommended strategy recommends a desirable behavior from three predefined plans according to intrinsic parameters, while the rating update rule involves the update of ratings of both users, and uses differential punishments that punish users with different ratings differently. By quantifying necessary and sufficient conditions for a sustainable social norm, we formulate the problem of designing an optimal two-sided rating protocol that maximizes the social welfare among all sustainable protocols, provide design guidelines for optimal two-sided rating protocols and a low-complexity algorithm to select optimal design parameters in an alternate manner. Finally, illustrative results show the validity and effectiveness of our proposed protocol designed for service exchange dilemma in crowdsourcing.