Optimization of orbital assignment and specification of service areas in satellite communications

The mathematical nature of the orbital and frequency assignment problem for communications satellites is explored, and it is shown that choosing the correct permutations of the orbit locations and frequency assignments is an important step in arriving at values which satisfy the signal-quality requirements. Two methods are proposed to achieve better spectrum/orbit utilization. The first, called the delta S concept, leads to orbital assignment solutions via either mixed-integer or restricted basis entry linear programming techniques; the method guarantees good single-entry carrier-to-interference ratio results. In the second, a basis for specifying service areas is proposed for the Fixed Satellite Service. It is suggested that service areas should be specified according to the communications-demand density in conjunction with the delta S concept in order to enable the system planner to specify more satellites and provide more communications supply

A Survey of Air-to-Ground Propagation Channel Modeling for Unmanned Aerial Vehicles

In recent years, there has been a dramatic increase in the use of unmanned aerial vehicles (UAVs), particularly for small UAVs, due to their affordable prices, ease of availability, and ease of operability. Existing and future applications of UAVs include remote surveillance and monitoring, relief operations, package delivery, and communication backhaul infrastructure. Additionally, UAVs are envisioned as an important component of 5G wireless technology and beyond. The unique application scenarios for UAVs necessitate accurate air-to-ground (AG) propagation channel models for designing and evaluating UAV communication links for control/non-payload as well as payload data transmissions. These AG propagation models have not been investigated in detail when compared to terrestrial propagation models. In this paper, a comprehensive survey is provided on available AG channel measurement campaigns, large and small scale fading channel models, their limitations, and future research directions for UAV communication scenarios

Sulfur amino acids and skeletal muscleNutition and skeletal muscle

Part IIINUTRITION AS A THERAPEUTICAL TOOL FOR SKELETAL MUSCLESection 4: Amino Acid SupplementsMethionine and cysteine are the two sulfur amino acids amongst the 20 standard ones incorporated into proteins. In addition to the dietary supply, cysteine can be synthetized from methionine and serine mainly in the liver but not in skeletal muscle. A large part of the whole body flux of methionine transmethylation contributes to the synthesis of creatine and carnitine. Cysteine is the rate-limiting substrate of the synthesis of glutathione and the precursor of taurine, coenzyme A, reduced and oxidized inorganic sulfurs. Only the coenzyme A synthesis pathway is complete in skeletal muscle. Skeletal muscle sulfur amino acid metabolism depends on the arterial availability of methionine and cysteine providers (cysteine, cystine, glutathione, other peptides). Creatine, cartinine, and coenzyme A are essential for ATP production and regeneration, and taurine plays also a role in muscle physiology. Conceptually, supplementations with sulfur amino acids or precursors might palliate some muscle impairments