E-MAC: an evolutionary solution for collision avoidance in wireless ad hoc networks

Transmission collision is a main cause of throughput degradation and non-deterministic latency in wireless networks. Existing collision-avoidance mechanisms for distributed wireless networks are mostly based on the random backoff strategy, which cannot guarantee collision-free accesses. In this paper, we design a simple collision-avoidance MAC (E-MAC) for distributed wireless networks that can iteratively achieve collision-free access. In E-MAC, each transmitter will adjust its next transmission time according to which part of its packets suffering from the collision. And the iteration of this adjustment will quickly lead group of nodes converging to a collision-free network. E-MAC does not require any central coordination or global time synchronization. It is scalable to new entrants to the network and variable packet lengths. And it is also robust to system errors, such as inaccurate timing.Transmission collision is a main cause of throughput degradation and non-deterministic latency in wireless networks. Existing collision-avoidance mechanisms for distributed wireless networks are mostly based on the random backoff strategy, which cannot guarantee collision-free accesses. In this paper, we design a simple collision-avoidance MAC (E-MAC) for distributed wireless networks that can iteratively achieve collision-free access. In E-MAC, each transmitter will adjust its next transmission time according to which part of its packets suffering from the collision. And the iteration of this adjustment will quickly lead group of nodes converging to a collision-free network. E-MAC does not require any central coordination or global time synchronization. It is scalable to new entrants to the network and variable packet lengths. And it is also robust to system errors, such as inaccurate timing

Second post-Newtonian approximation of scalar-tensor theory of gravity

Deep space laser ranging missions like ASTROD I (Single-Spacecraft Astrodynamical Space Test of Relativity using Optical Devices) and ASTROD, together with astrometry missions like GAIA and LATOR will be able to test relativistic gravity to an unprecedented level of accuracy. More precisely, these missions will enable us to test relativistic gravity to $10^{-7}-10^{-9}$, and will require 2nd post-Newtonian approximation of relevant theories of gravity. The first post-Newtonian approximation is valid to $10^{-6}$ and the second post-Newtonian is valid to $10^{-12}$ in the solar system. The scalar-tensor theory is widely discussed and used in tests of relativistic gravity, especially after the interests in inflation, cosmological constant and dark energy in cosmology. In the Lagrangian, intermediate-range gravity term has a similar form as cosmological term. Here we present the full second post-Newtonian approximation of the scalar-tensor theory including viable examples of intermediate-range gravity. We use Chandrasekhar's approach to derive the metric coefficients and the equation of the hydrodynamics governing a perfect fluid in the 2nd post-Newtonian approximation in scalar-tensor theory; all terms inclusive of $O(c^{-4})$ are retained consistently in the equation of motion.Comment: 20 pages, COSPAR2006 H0.1-

Machine Learning-Aided Operations and Communications of Unmanned Aerial Vehicles: A Contemporary Survey

The ongoing amalgamation of UAV and ML techniques is creating a significant synergy and empowering UAVs with unprecedented intelligence and autonomy. This survey aims to provide a timely and comprehensive overview of ML techniques used in UAV operations and communications and identify the potential growth areas and research gaps. We emphasise the four key components of UAV operations and communications to which ML can significantly contribute, namely, perception and feature extraction, feature interpretation and regeneration, trajectory and mission planning, and aerodynamic control and operation. We classify the latest popular ML tools based on their applications to the four components and conduct gap analyses. This survey also takes a step forward by pointing out significant challenges in the upcoming realm of ML-aided automated UAV operations and communications. It is revealed that different ML techniques dominate the applications to the four key modules of UAV operations and communications. While there is an increasing trend of cross-module designs, little effort has been devoted to an end-to-end ML framework, from perception and feature extraction to aerodynamic control and operation. It is also unveiled that the reliability and trust of ML in UAV operations and applications require significant attention before full automation of UAVs and potential cooperation between UAVs and humans come to fruition.Comment: 36 pages, 304 references, 19 Figure

Calcium and Calmodulin Involve in Mycorrhizal and Root Development in Trifoliate Orange Colonized by Rhizophagus intraradices

A pot experiment was made to study effects of ethylene glycol tetraacetic acid (EGTA, an inhibitor of Ca2+) and trifluoperazine (TFP, an inhibitor of calmodulin (CaM) on mycorrhizal colonization, growth performance, and chlorophyll, sucrose and glucose concentrations of four-month-old trifoliate orange (Poncirus trifoliata) seedlings under mycorrhization with Rhizophagus intraradices. Exogenous EGTA and TFP notably inhibited root mycorrhizal colonization, and the addition of EGTA also decreased soil hyphal length. In general, EGTA treatment decreased but TFP increased easily extractable glomalin-related soil protein (EE-GRSP) and total GRSP (T-GRSP) concentrations. In addition, EGTA and TFP applications generally significantly inhibited growth performance (height, stem diameter, leaf number, and shoot and root biomass), root traits (total length, surface area, volume, and number of 1st, 2nd and 3rd order lateral root), and chlorophyll a,b and a+b concentrations, the mycorrhizal inoculation generally reversed the negative effects and markedly increased these variables, irrespective of whether the seedlings were applied by inhibitors or not. EGTA and TFP treatments generally inhibited sucrose and glucose levels of leaf and root, except that TFP application notably increased root glucose in AM and non-AM seedlings. AMF inoculation resulted in carbohydrate modification: decrease in leaf sucrose, increase in root sucrose and leaf glucose, as well increase in root glucose under no-inhibitor and EGTA conditions and decrease in root glucose under TFP. It suggests that Ca2+ and CaM were involved in mycorrhizal and root development in trifoliate orange