Song et al. [20] proposed an improved corona model with levels for analyzing sensors with adjustable transmission ranges in WSNs with circular multi-hop deployment. They considered that the right transmission ranges of sensors in each corona is the decision factor for optimizing the network lifetime after nodes deployment. They also proved that searching optimal transmission ranges of sensors among all coronas is a multi-objective optimization problem, which is NP hard. Therefore, the authors proposed a centralized algorithm and a distributed algorithm for assigning the transmission ranges of sensors in each corona for different node distributions. The two algorithms can not only reduce the searching complexity but also obtain results approximated to the optimal solution.

Li and Mohapatra [11] developed a mathematical model to analyze the energy hole problem in a circular WSN and investigated the effect of several possible schemes that aim to mitigate the energy hole problem, such as deployment assistant, data compression and data aggregation. They assumed that nodes are uniformly and randomly distributed, and each node continuously generates constant bit rate data. Energy lost in data sensing, data transmission and reception is considered. The simulation results confirmed that hierarchical deployment, data aggragation and data compression can alleviate the energy hole problem, while under the same network diameter conditions, higher data rates will worsen the energy hole problem and higher node density cannot prolong the network lifetime.

Olariu and Stojmenovi? [12] were the first to study how to avoid the energy hole problem in WSNs. They investigated the theoretical aspects of uneven energy depletion problem in sink-based Carfilzomib WSNs with uniform node distribution and constant data reporting. They assumed an energy consumption model governed by E = d�� + c, where d is the transmission range and c is a positive constant parameter. They concluded that uneven energy depletion is intrinsic to the system and no routing strategy can avoid energy hole around the sink when �� = 2. For larger values of ��, the uneven energy consumption can be prevented by judicious system design and the energy consumption is suboptimally balanced across the network.

Lian et al. [13] proposed the SSEP-Non-uniform Sensor (SSEP-NS) distribution model and the SSEP-NS routing protocol to increase the network data capacity. The SSEP-

In the last years the employment of glucose oxidase (GOD) in glucose optical sensing has been largely investigated for clinical and GSK-3 industrial applications [1�C8].