3,556 research outputs found
Cooperative medium access control based on spectrum leasing
Based on cooperative spectrum leasing, a distributed “win–win” (WW) cooperative framework is designed to encourage the licensed source node (SN) to lease some part of its spectral resources to the unlicensed relay node (RN) for the sake of simultaneously improving the SN’s achievable rate and for reducing the energy consumption (EC). The potential candidate RNs carry out autonomous decisions concerning whether to contend for a cooperative transmission opportunity, which could dissipate some of their battery power, while conveying their traffic in light of their individual service requirements. Furthermore, a WW cooperative medium-access-control (MAC) protocol is designed to implement the proposed distributed WW cooperative framework. Simulation results demonstrate that our WW cooperative MAC protocol is capable of providing both substantial rate improvements and considerable energy savings for the cooperative spectrum leasing system
Phase transitions in a holographic s+p model with backreaction
In a previous paper (arXiv:1309.2204, JHEP 1311 (2013) 087), we present a
holographic s+p superconductor model with a scalar triplet charged under an
SU(2) gauge field in the bulk. We also study the competition and coexistence of
the s-wave and p-wave orders in the probe limit. In this work we continue to
study the model by considering the full back-reaction The model shows a rich
phase structure and various condensate behaviors such as the "n-type" and
"u-type" ones, which are also known as reentrant phase transitions in condensed
matter physics. The phase transitions to the p-wave phase or s+p coexisting
phase become first order in strong back-reaction cases. In these first order
phase transitions, the free energy curve always forms a swallow tail shape, in
which the unstable s+p solution can also play an important role. The phase
diagrams of this model are given in terms of the dimension of the scalar order
and the temperature in the cases of eight different values of the back reaction
parameter, which show that the region for the s+p coexisting phase is enlarged
with a small or medium back reaction parameter, but is reduced in the strong
back-reaction cases.Comment: 15 pages(two-column), 9 figure
The Research of Static Var Compensator's Time Characteristics and System-level Model of Controlled Current Source
AbstractIn the status of lacking research on response time of static var compensator (SVC), this paper established the controlled current source model which can achieve the same effect in response time and reactive compensation with the physical model of SVC by analyzing of characteristics in reactive power compensation and the response of the static var compensator (SVC) physical model. Through the time module in control signal of controlled current source, it can accurately calculate the response time of SVC. It tested the consistency of two models through the simulation of a rolling mill start experiment in PSCAD
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Repeated evolution of durophagy during ichthyosaur radiation after mass extinction indicated by hidden dentition.
Marine tetrapods quickly diversified and were established as marine top predators after the end-Permian Mass extinction (EPME). Ichthyosaurs were the forerunner of this rapid radiation but the main drivers of the diversification are poorly understood. Cartorhynchus lenticarpus is a basal ichthyosauriform with the least degree of aquatic adaptation, holding a key to identifying such a driver. The unique specimen appeared edentulous based on what was exposed but a CT scanning revealed that the species indeed had rounded teeth that are nearly perpendicular to the jaw rami, and thus completely concealed in lateral view. There are three dental rows per jaw ramus, and the root lacks infoldings of the dentine typical of ichthyopterygians. The well-developed and worn molariform dentition with three tooth rows supports the previous inference that the specimen is not of a juvenile. The premaxilla and the corresponding part of the dentary are edentulous. Molariform dentition evolved three to five times independently within Ichthyosauriformes in the Early and Middle Triassic. Convergent exploitation of hard-shelled invertebrates by different subclades of ichthyosauriforms likely fueled the rapid taxonomic diversification of the group after EPME
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