Sources and significance of variation in basal,summit and maximal metabolic rates in birds

The rates at which birds use energy may have profound effects on fitness, thereby influencing physiology, behavior, ecology and evolution. Comparisons of standardized metabolic rates （e.g., lower and upper limits of metabolic power output） present a method for elucidating the effects of ecological and evolutionary factors on the interface between physiology and life history in birds. In this paper we review variation in avian metabolic rates [basal metabolic rate （BMR; minimum normothermic metabolic rate）, summit metabolic rate （Msum; maximal thermoregulatory metabolic rate）, and maximal metabolic rate （MMR; maximal exercise metabolic rate）], the factors associated with this variation, the evidence for functional links between these metabolic traits, and the ecological and evolutionary significance of avian metabolic diversity. Both lower and upper limits to metabolic power production are phenotypically flexible traits, and vary in association with numerous ecological and evolutionary factors. For both inter- and intraspecific comparisons, lower and upper limits to metabolic power production are generally upregulated in response to energetically demanding conditions and downregulated when energetic demands are relaxed, or under conditions of energetic scarcity. Positive correlations have been documented between BMR, Msum and MMR in some, but not all studies on birds, providing partial support for the idea of a functional link between lower and upper limits to metabolic power production, but more intraspecific studies are needed to determine the robustness of this conclusion. Correlations between BMR and field metabolic rate （or daily energy expenditure） in birds are variable, suggesting that the linkage between these traits is subject to behavioral adjustment, and studies of the relationship between field and maximal metabolic rates are lacking. Our understanding of avian metabolic diversity would benefit from future studies of： （1） the functional and mechanistic links between lower and upper limits of metabolic power output; （2） the environmental and ecological cues driving phenotypically flexible metabolic responses, and how responses to such cues might impact population responses to climate change; （3） the shapes of metabolic reaction norms and their association with environmental variability; and （4） the relationship of metabolic variation to fitness, including studies of repeatability and heritability of minimum and maximum metabolic power output [Current Zoology 56 （6）： 741-758, 2010].

Joint Trajectory and Power Optimization for Securing UAV Communications Against Active Eavesdropping

Due to both of jamming and eavesdropping,active eavesdroppers can induce more serious security threats to unmanned aerial vehicle(UAV)-enabled communications.This paper considers a secure UAV communication system including both the downlink(DL)and uplink(UL)transmissions,where the confidential information is transmitted between a UAV and a ground node in the presence of an active eavesdropper.We aim to maximize the average secrecy rates of the DL and UL communications,respectively,by jointly optimizing the UAV trajectory and the UAV/ground node’s transmit power control over a given flight period.Due to the non-convexity of the formulated problems,it is difficult to obtain globally optimal solutions.However,we propose efficient iterative algorithms to obtain high-quality suboptimal solutions by applying the block coordinate descent and successive convex optimization methods.Simulation results show that the joint optimization algorithms can effectively improve the secrecy rate performance for both the DL and UL communications,as compared with other baseline schemes.The proposed schemes can be considered as special cases of UAV-assisted non-orthogonal multiple access(NOMA)networks.

Resource Allocation Based on User Pairing and Subcarrier Matching for Downlink Non-Orthogonal Multiple Access Networks

The traditional orthogonal multiple access(OMA)is unable to satisfy the needs of large number of smart devices.To increase the transmission rate in the limited spectrum resource,implementation of both non-orthogonal multiple access(NOMA)and successive interference cancelation(SIC)is essential.In this paper,an optimal resource allocation algorithm in NOMA is proposed to maximize the total system rate in a multi-sector multi-subcarrier relay-assisted communication network.Since the original problem is a non-convex problem with mixed integer programming which is non-deterministic polynomial-time(NP)-hard,a three-step solution is proposed to solve the primal problem.Firstly,we determine the optimal power allocation of the outer users by using the approach of monotonic discrimination,and then the optimal user pairing is determined.Secondly,the successive convex approximation(SCA)method is introduced to transform the non-convex problem involving central users into convex one,and the Lagrangian dual method is used to determine the optimal solution.Finally,the standard Hungarian algorithm is utilized to determine the optimal subcarrier matching.The simulation results show that resource allocation algorithm is able to meet the user performance requirements with NOMA,and the total system rate is improved compared to the existing algorithms.

Distributed Spectrum Sharing Scheme for Multiuser Orthogonal Frequency-Division Multiplexing Cognitive Radio Networks

This paper presents a novel spec- trum sharing design aiming at optimising the performance of a Multiuser Orthogonal Freq- uency-Division Multiplexing （MU-OFDM） Co- gnitive Radio Network （CRN） that consists of multiple secondary Transmitter-Receiver （Tx-Rx） pairs. For most MU-OFDM systems, the Exc- lusive Subchannel Assignment （ESA） is an efficient resource allocation method. Noneth- eless, it is inappropriate for the network consi- dered in this paper, because subchannels shar- ing among secondary Tx-Rx pairs can further improve the system performance. We investi- gate the Weighted Sum Rate （WSR） maximi- zation problem under the Shared Subchannel Assignment （SSA）, where each subchannel is shared by multiple secondary Tx-Rx pairs. With Lagrangian duality technique, we decompose the original resource allocation problem into sev- eral sub-problems on each subchannel and pro- pose a duality-based suhchannel sharing ap- proach. For practical realisation in the cogni- tive systems without central control entity, a distributed duality-based WSR maximization scheme is presented. Simulation results mani- fest that the proposed scheme achieves sig- nificantly better performance than ESA duality scheme.

Rate optimization using low complex methods with reconfigurable intelligent surfaces

With the help of a developing technology called reconfigurable intelligent surfaces(RISs),it is possible to modify the propagation environment and boost the data rates of wireless communication networks.In this article,we optimized the phases of the RIS elements and performed a fair power allocation for each subcarrier over the full bandwidth in a single-input-single-output(SISO)wideband system where the user and the access point(AP)are provided with a single antenna.The data rate or its equivalent channel power is maximized by proposing different low-complex algorithms.The strongest tap maximization(STM)and power methods are compared with the semidefinite relaxation(SDR)method in terms of computational complexity and data rate performance.Runtime and complexity analysis of the suggested methods are computed and compared to reveal the actual time consumption and the required number of operations for each method.Simulation results show that with an optimized RIS,the sum rate is 2.5 times higher than with an unconfigured surface,demonstrating the RIS's tremendous advantages even in complex configurations.The data rate performance of the SDR method is higher than the power method and less than the STM method but with higher computational complexity,more than 6 million complex operations,and 50 min of runtime calculations compared with the other STM and power optimization methods.

Seasonal Variation and Correlation with Environmental Factors of Photosynthesis and Water Use Efficiency of Juglans regia and Ziziphus jujuba

Both the photosynthetic light curves and CO2 curves of Juglans regia L. and Ziziphus jujuba Mill. var. spinosa in three seasons were measured using a LI-6400 portable photosynthesis system. The maximal net photosynthetic rate （Amax）, apparent quantum efficiency（φ）, maximal carboxylation rate （Vcmax） and water use efficiency （WUE） of the two species were calculated based on the curves. The results showed that Amax of J. regia reached its maximum at the late-season, while the highest values of Amax of Z. jujuba occurred at the mid-season. The Amax of J. regia was more affected by relative humidity （RH） of the atmosphere, while that of Z. jujuba was more affected by the air temperature. Light saturation point （LSP） and Light compensation point （LCP） of J. regia had a higher correlation with RH of the atmosphere, those of Z. jujuba, however, had a higher correlation with air temperature. Vcmax of both J. regia and Z. jujuba had negative correlation with RH of the atmosphere. WUE of J. regia would decrease with the rise of the air temperature while that of Z. jujuba increased. Thus it could be seen that RH, temperature and soil moisture had main effect on photosynthesis and WUE of J. regia and Z. jujuba. Incorporating data on the physiological differences among tree species into forest carbon models will greatly improve our ability to predict alterations to the forest carbon budgets under various environmental scenarios such as global climate change, or with differing species composition.

Prove the Minimal Delay of Complex Orthogonal Space-Time Block Code by Hadamard Matrix

The complex orthogonal designs with maximal rates and minimal delays is an open problem for space-time block code. Maximal rate can effectively transmit symbols to the lonest distance in the space dimension ; and minimal delay is the least decoding delay in the time dimension. Many authors have observed that regarding the complex orthogonal designs for space-time block codes with the antennas n = 4k （ k ∈ N ）, its minimal delay is the same as that for n - 4k -1. However none was able to prove it. In this paper, we use the characteristics of Hadamard matrix to prove this property to fulfill this vacancy.

Size-related effects and the influence of metabolic traits and morphology on swimming performance in fish

Energy metabolism fuels swimming and other biological processes.We compared the swimming performance and energy metabolism within and across eight freshwater fish species.Using swim tunnel respirometers,we measured the standard metabolic rate(SMR)and maximum metabolic rate(MMR)and calculated the critical swimming speed(Ucrit).We accounted for body size,metabolic traits,and some morphometric ratios in an effort to understand the extent and underlying causes of variation.Body mass was largely the best predictor of swimming capacity and metabolic traits within species.Moreover,we found that predictive models using total length or SMR,in addition to body mass,signicantly in creased the explained variation of Ucrit and MMR in certain fish species.These predictive models also underlined that,once body mass has been accounted for,Ucrit can be independently affected by total length or MMR.This study exemplifies the utility of multiple regression models to assess within-species variability.At interspecific level,our results showed that variation in UcriX can partly be explained by the variation in the interrelated traits of MMR,finen ess,and muscle ratios.Among the species studied,bleak Al burn us alburnus performed best in terms of swimming performance and efficiency.By contrast,pumpkinseed Lepomis gibbosus showed very poor swimming performance,but attained lower mass-specific cost of transport(MCOT)than some rheophilic species,possibly reflecting a cost reduction strategy to compensate for hydrod yn amic disadvantages.In con elusion,this study provides insight into the key factors in fluenci ng the swimming performa nee of fish at both intra-and in terspecific levels.