In cognitive wireless networks where secondary users (SUs) opportunistically access spectral white spaces of primary users (PUs), there exists an inherent tradeoff between sensing and transmission due to the competing goals of PU protection and SU access maximization. This paper studies means of sensing-transmission for SUs to better manage the competing goals by defining utility function to reward the SU for successful packet transmissions and to penalize it for colliding with PU. To maximize the SU utility, we present a threshold-based sensing-transmission structure that is optimal under a technical constraint. Both perfect sensing and imperfect sensing are considered, with or without SU acknowledgement of reception. This SU access scheme optimizes SU access efficiency while protecting PU performance. It sets a benchmark and provides insight for the design of sensing-transmission control in cognitive networks such as IEEE 802.22.
Meshless methods based on collocation with radial basis functions (RBFs) are investigated in detail in this paper. Both globally supported and compactly supported radial basis functions are used with collocation to solve partial differential equations (PDEs). Using RBFs as a meshless collocation method to solve PDEs possesses some advantages. It is a truly mesh-free method, and is space dimension independent. Furthermore, in the context of scattered data interpolation it is known that some radial basis functions have spectral convergence orders.This study shows that the accuracy of derivatives of interpolating functions are usually very poor on boundary of domain when a direct collocation method is used, therefore it will result in signi®cant error in solving a PDE with Neumann boundary conditions. Based on this fact, a Hermite type collocation method is proposed in this paper, in which both PDEs and prescribed traction boundary conditions are imposed on prescribed traction boundary. Numerical studies shows that the Hermite type collocation method improve the accuracy signi®cantly.
Summary 1.Inasmuch as virtually all studies on mortality and reproduction in insects are conducted under conditions in which food availability is constant, little is known about the demographic response of insects to variable food environments. For example, it is not known if and to what extent the life expectancy of insects subjected to shortages of high-quality food will increase and/or whether this increase is associated with major decreases in lifetime reproduction. 2. Therefore cohorts of 100 individual female medflies were subjected to different sets of conditions of protein availability (interspersed with sugar-only diets) including ad libitum sugar-only (no protein), ad libitum protein and full (protein) diet either every 2nd, 4th, 6th, 11th or 21st day, as well as two lag-treatments (1 day full diet followed by 30 days sugar-only, followed by one of two cyclical treatments). 3. Both life expectancy and lifetime reproduction were strongly affected by specific treatments. Specifically (i) mortality was inversely related to frequency of protein availability whereas lifetime reproduction was directly related; (ii) distinct cycles in reproduction began to appear when food pulse cycles were as short as every 4 days. However, egg-laying peaks and troughs were particularly pronounced in the 10-and 20-day food pulse cycles; (iii) the peak and trough levels were inversely related to cycle length; and (iv) the within-cycle height was independent of cycle length, occurring 4 days after protein food was made available to the cohort whether the cycle length was 5, 10 or 20 days. 4. The results shed new light on the within-and between-cycle and lifetime dynamics of reproduction when insects are subjected to variable food environments and indicate that medfly females track food level very closely.
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