Nevertheless, there still exist many problems, such as the serious data sparsity problem and the cold start problem.
Actually, for such emerging network architecture, there still exist many problems to be solved to guarantee the reliable transmission.
However, for such emerging architecture, there still exist many problems to be solved to guarantee the reliable transmission.
However, there exist many problems that require further investigation, the chief among which is the direction of trend components decomposed from annual streamflow series and is always difficult to ascertain.
Additionally, there exist many problems that cannot be ignored when big data is applied to safety science, most outstanding of which is lack of universal supporting theory that guides how to apply big data to safety science research like methods, principles and approaches, etc.
Though the new technologies have shown great advantages compared with amorphous silicon technologies for flexible electronics, there still exist many problems, for example, some pollution and waste still cannot be avoided during screen printing, printer setups are also very expensive, the defective products produced by these methods are hard to repair, etc.
Actually, it is known that there exist many open problems which can be derived from the original problem.
There exists many heuristics for solving this problem [see, e.g. Johnson and Trick, 1996; Kubale, 2004] based on greedy selection of a maximal independent set.
However, this autonomous control method is not widely applied among numerous experimental microgrids, because there still exist many practical problems, such as the dynamic response speed, the impact of control parameters on system stability, the capability to deal with unbalanced and non-linear loads, and control strategies under fault conditions.
On the one hand, the constrained optimization equation of WCB is a nonconvex NP-hard problem; although there exists many methods [12, 19] to solve it, there is no closed-form solution until now.
