Stabilization of large space structures by linear reluctance actuators

Application of magnetic forces are considered for stabilization of vibrations of flexible space structures. Three electromagnetic phenomena are studied, such as: (1) magnetic body force; (2) reluctance torque; and (3) magnetostriction, and their application is analyzed for stabilization of a beam. The magnetic body force actuator uses the force that exists between poles of magnets. The reluctance actuator is configured in such a way that the reluctance of the magnetic circuit will be minimum when the beam is straight. Any bending of the beam increases the reluctance and hence generates a restoring torque that reduces bending. The gain of the actuator is controlled by varying the magnetizing current. Since the energy density of a magnetic device is much higher compared to piezoelectric or thermal actuators, it is expected that the reluctance actuator will be more effective in controlling the structural vibrations

Electrostatic built-in fields in wurtzite III-N nanostructures: impact of growth plane on second-order piezoelectricity

In this work we present a detailed analysis of the second-order piezoelectric effect in wurtzite III-N heterostructures, such as quantum wells and quantum dots, grown on different substrate orientations. Our analysis is based on a continuum model using a here derived analytic expression for the second-order piezoelectric polarization vector field as a function of the incline angle theta to the wurtzite c axis. This expression allows for a straightforward implementation in existing quantum well and quantum dot codes. Our calculations on III-N quantum well systems reveal that especially for semipolar structures with high incline angle values (55 degrees <= theta <= 80 degrees and 105 degrees <= theta <= 120 degrees), second-order piezoelectricity noticeably contributes to the overall electric built-in field. For instance, in an InGaN/GaN multiple quantum well system with 22% In, the electric field increases by approximately 20% due to second-order piezoelectricity. Overall, when including second-order piezoelectric effects in the calculation of electric fields in GaN/AlN and InGaN/GaN quantum well systems an improved agreement between our theory and experimental literature data is observed. When studying quantum dots, at least for the here considered model geometry and growth planes, we observe that for GaN/AlN structures second-order effects are of secondary importance. The situation is different for non-c-plane In0.2Ga0.8N/GaN quantum dots. For example, inside a nonpolar In0.2Ga0.8N/GaN dot the built-in potential arising from second-order piezoelectricity is comparable in magnitude to the built-in potential originating from spontaneous and first-order piezoelectric polarization, but opposite in sign. This feature leads to a change in the built-in potential profile both in and around the In0.2Ga0.8N/GaN quantum dot structure, which in general is relevant for electronic and optical properties of these systems

Managing interactions between household food security and preschooler health:

Food security does not assure good nutrition. The nutritional status of an individual is influenced not only by food but also by nonfood factors, such as clean water, sanitation, and health care. The effect of all of these factors must be considered in efforts to rid the world of malnutrition. Food security will result in good nutrition only if nonfood factors are effectively dealt with. In this paper, Lawrence Haddad, Saroj Bhattarai, Maarten Immink, and Shubh Kumar show how malnutrition among preschool children is determined by a complex interaction of illness and lack of food. The authors look at three countries —Ethiopia, Pakistan, and the Philippines — to study how food availability and diarrhea interact and what this interaction means for preschooler malnutrition. Their results show that the links between food consumption, diarrhea, and malnutrition are stronger than most economic studies have assumed. When diarrhea is prevalent, the effects of food shortages on child malnutrition are worse, and when food is scarce, the effects of diarrhea on child malnutrition are worse.Food security Ethiopia., Malnutrition in children Ethiopia., Food security Pakistan., Malnutrition in children Pakistan., Food security Philippines., Malnutrition in children Philippines.,