Steering of fogging: control of humidity: temperature or transpiration

Fogging systems are increasingly used to cool greenhouses and prevent water stress. More recently, fogging systems are applied also in relatively low radiation environments (such as The Netherlands), for a better control of product quality than whitewashing and to reduce need for natural ventilation ¿ thus allowing for higher CO2 concentrations to be maintained in the greenhouse. Most commonly the steering of such systems is done by setting an upper limit to the deficit of specific humidity that, whenever exceeded, triggers the fogging system. In both cases, however, one may wonder whether static and pre-fixed set points are the most effective choice. In the experiment presented in this paper, fogging and venting were controlled with the purpose of steering crop transpiration. The desired transpiration rate was the input of an algorithm that calculated on-line the required humidity and air temperature set points in view of the current weather factors. The set points were then the input of a standard P-controller that calculated vent opening and time of operation of the fogging system. In this paper, the resulting climate and actuator control operations are discussed and compared with a similar greenhouse controlled in a traditional fashion. The study concluded that a desired crop transpiration rate (an all-round indicator of crop well-being) could be used to select dynamic set points for the climate control in a greenhouse equipped with a fogging system

Sliding set-points of immune responses for therapy of autoimmunity

Although recent developments in the treatment of autoimmune disease have dramatically improved patient outcomes, these medications are not curative. Two studies in this issue demonstrate the feasibility of curing spontaneous autoimmunity in animal models via short-term enhancement of naturally arising regulatory T (T reg) cells, a subset of CD4+ T cells needed for maintaining self-tolerance. Importantly, these therapies seemed to generate a new equilibrium, or “set-point,” at which self-tissue damage no longer occurred long after the drug was eliminated from the body

Digital control of diode laser for atmospheric spectroscopy

A system is described for remote absorption spectroscopy of trace species using a diode laser tunable over a useful spectral region of 50 to 200 cm(-1) by control of diode laser temperature over range from 15 K to 100 K, and tunable over a smaller region of typically 0.1 to 10 cm(-1) by control of the diode laser current over a range from 0 to 2 amps. Diode laser temperature and current set points are transmitted to the instrument in digital form and stored in memory for retrieval under control of a microprocessor during measurements. The laser diode current is determined by a digital to analog converter through a field effect transistor for a high degree of ambient temperature stability, while the laser diode temperature is determined by set points entered into a digital to analog converter under control of the microprocessor. Temperature of the laser diode is sensed by a sensor diode to provide negative feedback to the temperature control circuit that responds to the temperature control digital to analog converter

Propagation of singularities for weak KAM solutions and barrier functions

This paper studies the structure of the singular set (points of nondifferentiability) of viscosity solutions to Hamilton-Jacobi equations associated with general mechanical systems on the n-torus. First, using the level set method, we characterize the propagation of singularities along generalized characteristics. Then, we obtain a local propagation result for singularities of weak KAM solutions in the supercritical case. Finally, we apply such a result to study the propagation of singularities for barrier functions

Distributed control of wind farm power set points to minimise fatigue loads

The quantity and size of wind farms continue to grow as countries around the world strive to meet ambitious targets for renewable electricity generation such as the UK government's Net Zero target of increasing offshore wind energy from current levels (circa 6 GW) to circa 75 GW by 2050. With increasing size and quantity of wind farms, there is a growing requirement to use wind farm level control both to help with grid integration and to minimise the loads on the turbines in the farm. In this paper, a methodology of distributing power set points through a wind farm to minimise the loads on the turbines whilst meeting a delta power set point for the farm is presented. The methodology in this paper uses a hierarchical control structure, in which a network wind farm controller calculates the required change in wind farm power and then passes this value on to a distributed controller that defines the change in power required from each wind turbine. The network wind farm controller calculates a delta change in wind farm power that the wind farm holds in reserve. The distributed controller allocates the reductions in power output by first setting a baseline reduction that considers the steady state tower loads. The baseline is then adjusted to meet the required change in power, distributing the additional change in one of two ways; either proportional to the square of each turbines estimated wind speed or proportional to the initial baseline. Performance is assessed using the StrathFarm simulation tool. The wind turbine models incorporated into StrathFarm are sufficiently detailed to provide the tower and blade loads and the wind field model is sufficiently detailed to represent turbulence, wind shear, tower shadow and wakes and their interaction. The performance of the proposed wind farm controllers are assessed for a range of wind conditions for two 4x4 wind farms of 5MW wind turbines, one closely spaced (500m) and one less closely spaced (1000m). Both the accuracy of the change in power output from the wind farm and the change in turbines DELs are discussed. Depending on the wind conditions, the approach is found to reduce the tower and blade loads by about 10% more than the case in which each turbine is simply allocated the same change in power. There is good accuracy in the change in power at higher wind speeds. Below rated wind speed, wake effects reduce the accuracy of the change in power

HIV-1 transmitting couples have similar viral load set-points in Rakai, Uganda.

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Multi-input, multi-output regulator design for constant disturbances and non-zero set points with application to automatic landing in a crosswind

Undesirable steady offsets result when a stationary, linear regulator using state feedback is subjected to constant disturbances and/or non-zero setspoints. To eliminate these offsets, the disturbances and non-zero setpoints can be fed forward to the control. Only when the number of outputs is less than or equal to the number of control inputs can the outputs be maintained at arbitrary non-zero setpoints. The state and the disturbance may be estimated using a constant gain Kalman filter or by modeling the constant disturbances as exponentially correlated processes with long correlation times