Dark Energy from Cosmological Energy Conservation

The value of the gravitational wave energy density is unknown. Current progress in gravitational wave detection suggests that the energy density of the stochastic gravitational wave background (SGWB) will be estimated in the next decades. A derivation of its value is presented under the assumption that energy lost due to cosmic redshift is fully responsible for the energy gained by the cosmological constant in the expanding universe. This unknown nonlocal mechanism of energy conservation on the cosmic scale could explain dark energy and hint at a property of a theory of quantum gravity

Reduced overhead for intra-cluster and inter-cluster sensor-to-actor communications in IEEE 802.15.4 networks

International audienceThis paper proposes a novel way to enable sensor-to-actor communications in wireless sensor and actor networks (WSANs) that only requires a simple modification to the IEEE 802.15.4 header. Although this standard includes the definition of sensor-to-actor communication, it does not address how to provide it. Our proposal is able to provide this sensor-to-actor communication at the 802.15.4 MAC layer, thereby reducing the overhead of the additional network header, and achieving an important reduction of the energy consumption. In addition, avoiding the need of a network layer with full routing capabilities in the sensors provides further memory, processing and communications saving. Moreover, this paper considers two scenarios for sensor-to-actor communications: intra-cluster and inter-cluster. The former enables the communication among sensors/actors at the same wireless sensor and actor network, and the latter allows sensors/actors located in geographically separated cluster to communicate transparently as if they were in the same WSA